our websites and efficiently managing our operating costs, offset by investments we make in longer-term strategic initiatives, which generally require us to hire additional software engineers, computer scientists, and merchandisers. To increase product sales, we focus on improving all aspects of the customer experience, including lowering prices, improving availability, offering faster delivery times, increasing selection, increasing product categories, expanding product information, improving ease of use, and earning customer trust. We generally focus on growing gross profit and operating profit dollars rather than maximizing margin percentages. 

We also seek to efficiently manage shareholder dilution while maintaining the flexibility to issue shares for strategic purposes, such as financings and aligning employee compensation with shareholders’ interests. We utilize restricted stock units as our primary vehicle for equity compensation because we believe they align the interests of our shareholders and employees. In managing shareholder dilution, we include all stock awards outstanding, without regard to estimated forfeitures, consisting of vested and unvested awards and in-the-money and out-of-the-money stock options. Total shares outstanding plus outstanding stock awards were 435 million and 436 million at December 31, 2007 and 2006. These amounts exclude 14 million shares issuable upon conversion of our long-term debt. In 2007, we repurchased 6 million shares of our common stock under a repurchase program authorized by our Board of Directors. 

We seek to reduce our variable costs per unit and work to leverage our fixed costs. Our variable costs include product and content costs, payment processing and related transaction costs, picking, packaging, and preparing orders for shipment, transportation, customer service support, and most aspects of our marketing costs. Our fixed costs include the costs necessary to run our technology infrastructure, build, enhance, and add features to our websites and build and optimize our fulfillment centers. Variable costs generally change directly with sales volume, while fixed costs generally increase depending on the timing of capacity needs, geographic expansion, category expansion, and other factors. To decrease our variable costs on a per unit basis and enable us to lower prices for customers, we seek to increase our direct to publisher and manufacturer sourcing, maximize discounts available to us from suppliers and reduce defects in our processes. To minimize growth in fixed costs, we seek to improve process efficiencies and maintain a lean culture. 

Because of our model we are able to turn our inventory quickly and have a cash-generating operating cycle. On average, our high inventory velocity means we generally collect from our customers before our payments to suppliers come due. Inventory turnover was 13, 13, and 14 for 2007, 2006, and 2005. Inventory turnover has declined slightly over the last several years, primarily due to category expansion and changes in product mix, and our continuing focus on in-stock inventory availability. We expect some variability in inventory turnover over time