Statements and Supplementary Data—Note 6—Commitments and Contingencies” for additional discussion of our principal contractual commitments, as well as our pledged securities. Purchase obligations and open purchase orders, consisting of inventory and significant non-inventory commitments, were $1.5 billion at December 31, 2010. 

On average, our high inventory turnover means we collect from our customers before our payments to suppliers come due. Inventory turnover was 11, 12, and 12 for 2010, 2009, and 2008. We expect some variability in inventory turnover over time as it is affected by several factors, including category expansion and changes in our product mix, the mix of sales by us and by other sellers, our continuing focus on in- stock inventory availability, our investment in new geographies and product lines, and the extent to which we choose to utilize outsource fulfillment providers. 

We believe that current cash, cash equivalents, and marketable securities balances will be sufficient to meet our anticipated operating cash needs for at least the next 12 months. However, any projections of future cash needs and cash flows are subject to substantial uncertainty. See Item 1A of Part I, “Risk Factors.” We continually evaluate opportunities to sell additional equity or debt securities, obtain credit facilities, repurchase common stock, pay dividends, or repurchase, refinance, or otherwise restructure our debt for strategic reasons or to further strengthen our financial position. The sale of additional equity or convertible debt securities would likely be dilutive to our shareholders. In addition, we will, from time to time, consider the acquisition of, or investment in, complementary businesses, products, services, and technologies, which might affect our liquidity requirements or cause us to issue additional equity or debt securities. There can be no assurance that additional lines-of-credit or financing instruments will be available in amounts or on terms acceptable to us, if at all. 

Results of Operations 

We have organized our operations into two principal segments: North America and International. We present our segment information along the same lines that our chief executive reviews our operating results in assessing performance and allocating resources. 

Net Sales 

Sales increased 40%, 28%, and 29% in 2010, 2009, and 2008. Changes in currency exchange rates positively (negatively) affected net sales by $(86) million, $(182) million, and $127 million for 2010, 2009, and 2008. For a discussion of the effect on sales growth of exchange rates, see “Effect of Exchange Rates” below. 

The North America sales growth rate was 46%, 25%, and 26% in 2010, 2009, and 2008. The sales growth in each year primarily reflects increased unit sales, a larger base of sales in faster growing categories such as electronics and other general merchandise, and, in 2010, our adoption of the new accounting standard update (“ASU”) 2009-13 (see Item 8 of Part II, “Financial Statements and Supplementary Data—Note 1—Description of Business and Accounting Policies”). Increased unit sales were driven largely by our continued efforts to reduce prices for our