The preparation of financial statements in conformity with generally accepted accounting principles of the United States (“GAAP”) requires estimates and assumptions that affect the reported amounts of assets and liabilities, revenues and expenses, and related disclosures of contingent assets and liabilities in the consolidated financial statements and accompanying notes. The SEC has defined a company’s critical accounting policies as the ones that are most important to the portrayal of the company’s financial condition and results of operations, and which require the company to make its most difficult and subjective judgments, often as a result of the need to make estimates of matters that are inherently uncertain. Based on this definition, we have identified the critical accounting policies and judgments addressed below. We also have other key accounting policies, which involve the use of estimates, judgments, and assumptions that are significant to understanding our results. For additional information, see Item 8 of Part II, “Financial Statements and Supplementary Data—Note 1—Description of Business and Accounting Policies.” Although we believe that our estimates, assumptions, and judgments are reasonable, they are based upon information presently available. Actual results may differ significantly from these estimates under different assumptions, judgments, or conditions. 

Inventories 

Inventories, consisting of products available for sale, are primarily accounted for using the first-in first-out (“FIFO”) method, and are valued at the lower of cost or market value. This valuation requires us to make judgments, based on currently-available information, about the likely method of disposition, such as through sales to individual customers, returns to product vendors, or liquidations, and expected recoverable values of each disposition category. 

These assumptions about future disposition of inventory are inherently uncertain. As a measure of sensitivity, for every 1% of additional inventory valuation allowance at December 31, 2010 we would have recorded an additional cost of sales of approximately $33 million. 

Goodwill 

We evaluate goodwill for impairment annually or more frequently when an event occurs or circumstances change that indicates that the carrying value may not be recoverable. Our annual testing date is October 1. We test goodwill for impairment by first comparing the book value of net assets to the fair value of the reporting units. If the fair value is determined to be less than the book value, a second step is performed to compute the amount of impairment as the difference between the estimated fair value of goodwill and the carrying value. We estimate the fair value of the reporting units using discounted cash flows. Forecasts of future cash flow are based on our best estimate of future net sales and operating expenses, based primarily on expected category expansion, pricing, market segment share, and general economic conditions. Certain estimates of discounted cash flows involve businesses and geographies with limited financial history and developing revenue models. Changes in these forecasts could significantly