During 2011, in response to challenging business conditions, we initiated activities to reduce and contain spending, including reducing our workforce, consultants and discretionary expenses.

During 2009, we continued our multi-quarter plan to improve profitability and reduce and contain spending. We made progress against the initiatives that management set in 2007, continued our restructuring plan and executed activities with a focus on creating a more cost effective organization, with a greater percentage of variable costs. These activities included downsizing and consolidating some locations, reducing our workforce, consultants and discretionary expenses and realigning our sales organization and engineering groups.

In conjunction with these activities, we recognized restructuring charges (credits) of approximately $1.3 million, $(0.2) million and $4.5 million during the years ended December 31, 2011, 2010 and 2009, respectively. We also recognized inventory write-offs of $0.8 million and $1.5 million, included in cost of sales in the accompanying Consolidated Statement of Operations, related to a discontinued product line in our LED & Solar segment during the year ended December 31, 2011 and discontinued data storage products during the year ended December 31, 2009. Restructuring expense for the years ended December 31, 2011, 2010 and 2009 are as follows (in thousands):

During 2011, we recorded $1.3 million in personnel severance and related costs related to a companywide reorganization resulting in a headcount reduction of 65 employees. During 2009, we recorded $3.1 million in personnel severance and related costs resulting from a headcount reduction of 161 employees. These reductions in workforce included executives, management, administration, sales and service personnel and manufacturing employees' companywide.

During 2010, we had a change in estimate relating to one of our leased Data Storage facilities. As a result, we incurred a restructuring credit of $0.2 million, consisting primarily of the remaining lease payment obligations and estimated property taxes for a portion of the facility we will occupy, offset by a reduction in expected sublease income. We made certain assumptions in determining the credit, which included a reduction in estimated sublease income and terms of the sublease as well as the estimated discount rate to be used in determining the fair value of the remaining liability. We developed these assumptions based on our understanding of the current real estate market as well as current market interest rates. The assumptions are based on management's best estimates, and will be adjusted periodically if new information is obtained.

During 2009, we vacated our Data Storage facilities in Camarillo, CA. As a result, we incurred a $1.4 million restructuring charge, consisting primarily of the remaining lease payment obligations and estimated property taxes for the facility we vacated, offset by the estimated expected sublease income to be received. We made certain assumptions in determining the charge, which included estimated sublease income and terms of the sublease as well as the estimated discount rate to be used in determining the fair value of the liability. We developed these assumptions based on our understanding of the current real estate market as well as current market interest rates. The assumptions are based on management's best estimates, and will be adjusted periodically if new information is obtained.

The following is a reconciliation of the liability for the 2011, 2010 and 2009 restructuring charge from inception through December 31, 2011 (in thousands):

	LED & Solar			Data Storage			Unallocated Corporate			Total

Short-term liability
Beginning Balance January 1, 2009	$	36		$	270		$	1,859		$	2,165
Lease-related and other costs 2009		190			803			—			993
Personnel severance and related costs 2009		647			1,826			636			3,109

Total charged to accrual 2009		837			2,629			636			4,102

Lease-related and other credits 2010		—			(87	)		—			(87	)

Total credited to accrual 2010		—			(87	)		—			(87	)

Personnel severance and related costs 2011		672			51			311			1,034

Total charged to accrual 2011		672			51			311			1,034

Short-term/long-term reclassification 2009		—			148			1,084			1,232
Short-term/long-term reclassification 2010		—			123			536			659
Short-term/long-term reclassification 2011		—			58			—			58
Cash payments 2009		(677	)		(2,561	)		(1,982	)		(5,220	)
Cash payments 2010		(196	)		(344	)		(1,597	)		(2,137	)
Cash payments 2011		(138	)		(159	)		(553	)		(850	)

Balance as of December 31, 2011	$	534		$	128		$	294		$	956

Long-term liability
Beginning Balance January 1, 2009	$	—		$	—		$	1,620		$	1,620
Lease-related and other costs 2009		—			377			—			377
Lease-related and other credits 2010		—			(48	)		—			(48	)
Short-term/long-term reclassification 2009		—			(148	)		(1,084	)		(1,232	)
Short-term/long-term reclassification 2010		—			(123	)		(536	)		(659	)
Short-term/long-term reclassification 2011		—			(58	)		—			(58	)

Balance as of December 31, 2011	$	—		$	—		$	—		$	—

During 2011, we recorded a $0.6 million asset impairment charge in the fourth quarter for property, plant and equipment related to the discontinuance of a certain product line in our LED & Solar reporting unit.

During 2009, we recorded a $0.3 million asset impairment charge in the second quarter for property, plant and equipment no longer being utilized in our Data Storage reporting unit.

Minimum lease commitments as of December 31, 2011 for property and equipment under operating lease agreements (exclusive of renewal options) are payable as follows (in thousands):

Rent charged to operations amounted to $2.7 million, $1.7 million and $1.6 million in 2011, 2010 and 2009, respectively. In addition, we are obligated under such leases for certain other expenses, including real estate taxes and insurance.

We may, under certain circumstances, be obligated to pay up to $250,000 in connection with the implementation of a comprehensive plan of environmental remediation at our Plainview, New York facility. We have been indemnified by the former owner for any liabilities we may incur in excess of $250,000 with respect to any such remediation and have a liability recorded for this amount as of December 31, 2011. No comprehensive plan has been required to date. Even without consideration of such indemnification, we do not believe that any material loss or expense is probable in connection with any remediation plan that may be proposed.

We are aware that petroleum hydrocarbon contamination has been detected in the soil at the site of a facility formerly leased by us in Santa Barbara, California. We have been indemnified for any liabilities we may incur which arise from environmental contamination at the site. Even without consideration of such indemnification, we do not believe that any material loss or expense is probable in connection with any such liabilities.

The former owner of the land and building in Santa Barbara, California in which our former Metrology operations were located, which business (sold to Bruker on October 7, 2010), has disclosed that there are hazardous substances present in the ground under the building. Management believes that the comprehensive indemnification clause that was part of the purchase contract relating to the purchase of such land provides adequate protection against any environmental issues that may arise. We have provided Bruker indemnification as part of the sale.

We are involved in various legal proceedings arising in the normal course of our business. We do not believe that the ultimate resolution of these matters will have a material adverse effect on our consolidated financial position, results of operations or cash flows.

Our business depends in large part upon the capital expenditures of our top ten customers, which accounted for 79% and 80% of total accounts receivable at December 31, 2011 and 2010, respectively. Of such, HB LED and data storage customers accounted for approximately 58% and 19%, and 62% and 18%, respectively, of total accounts receivable at December 31, 2011 and 2010.

Customers who accounted for more than 10% of our aggregate accounts receivable or net sales are as follows:

We manufacture and sell our products to companies in different geographic locations. In certain instances, we require deposits for a portion of the sales price in advance of shipment. We perform periodic credit evaluations of our customers' financial condition and, where appropriate, require that letters of credit be provided on certain foreign sales arrangements. Receivables generally are due within 30-60 days, other than receivables generated from customers in Japan where payment terms generally range from 60-90 days. Our net accounts receivable balance is concentrated in the following geographic locations (in thousands):

We currently outsource certain functions to third parties, including the manufacture of all or substantially all of our new MOCVD systems, Data Storage systems and ion sources. We primarily rely on several suppliers for the manufacturing of these systems. We plan to maintain some level of internal manufacturing capability for these systems. The failure of our present suppliers to meet their contractual obligations under our supply arrangements and our inability to make alternative arrangements or resume the manufacture of these systems ourselves could have a material adverse effect on our revenues, profitability, cash flows, and relationships with our customers.

In addition, certain of the components and sub-assemblies included in our products are obtained from a single source or a limited group of suppliers. Our inability to develop alternative sources, if necessary, could result in a prolonged interruption in supply or a significant increase in the price of one or more components, which could adversely affect our operating results.