of refunds) were $33 million, $75 million, and $48 million for 2011, 2010, and 2009. As of December 31, 2011, our federal net operating loss carryforward was approximately $384 million. We also have approximately $273 million of federal tax credits potentially available to offset future tax liabilities. Once we utilize our federal net operating losses and tax credits, we expect cash paid for taxes to significantly increase. We endeavor to optimize our global taxes on a cash basis, rather than on a financial reporting basis. 

See Item 8 of Part II, “Financial Statements and Supplementary Data—Note 7—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 $3 billion at December 31, 2011. Purchase obligations and open purchase orders are generally cancelable in full or in part through the contractual provisions. 

On average, our high inventory turnover means we collect from our customers before our payments to suppliers come due. Inventory turnover was 10, 11, and 12 for 2011, 2010, and 2009. We expect 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 41%, 40%, and 28% in 2011, 2010, and 2009. Changes in currency exchange rates positively (negatively) affected net sales by $1.1 billion, $(86) million, and $(182) million for