in the period estimates are revised. We consider many factors when estimating expected forfeitures, including types of awards, employee class, and historical experience. Actual results and future estimates may differ substantially from our current estimates. 

The adoption of SFAS No. 123(R) resulted in a cumulative benefit from accounting change of $26 million in 2005, which reflects the net cumulative impact of estimating future forfeitures in the determination of period expense, rather than recording forfeitures when they occur as previously permitted. 

Stock-based compensation was $185 million, $101 million and $87 million during 2007, 2006, and 2005. The increase in stock-based compensation is primarily attributable to an increase in total stock compensation value granted to our employees. 

Other Operating Expense, Net 

Other operating expense, net, was $9 million and $10 million during 2007 and 2006, primarily attributable to amortization of other intangibles. Other operating expense, net, was $47 million in 2005, primarily attributable to our settlement of a patent lawsuit for $40 million, as well as amortization of other intangibles of $5 million. 

Income from Operations 

Income from operations was $655 million, $389 million, and $432 million during 2007, 2006, and 2005. The increase in 2007 from 2006 is primarily a result of the increased growth rate of our revenue and gross profit relative to operating expenses. The decrease in 2006 from 2005 is primarily a result of an increase in spending for technology and content. 

Interest Expense and Income 

The primary component of our net interest expense is the interest we incur on our long-term debt instruments, including a $899 million principal balance of our 4.75% Convertible Subordinated Notes and a €240 million ($350 million based on the exchange rate at December 31, 2007) principal balance of our 6.875% PEACS at December 31, 2007. Interest expense was $77 million, $78 million, and $92 million in 2007, 2006, and 2005, with declines primarily relating to principal repayments of $300 million and $265 million in 2006 and 2005. 

Our total long-term indebtedness was $1.3 billion at both December 31, 2007 and 2006. See Item 8 of Part II, “Financial Statements and Supplementary Data—Note 4—Long-Term Debt.” 

Our interest income was $90 million, $59 million, and $44 million during 2007, 2006, and 2005. We generally invest our excess cash in investment grade short- to intermediate-term fixed income securities and AAA-rated money market mutual funds. Our interest income corresponds with the average balance of invested funds and the prevailing rates we are earning on them, which vary depending on the geographies and currencies in which they are invested. 

Other Income (Expense), Net 

Other income (expense), net, was $(1) million, $(4) million, and $2 million, in 2007, 2006 and 2005, and consisted primarily of gains and losses on sales of marketable securities, foreign-currency transaction gains and losses, and other miscellaneous losses. 

Foreign-currency transaction gains and losses primarily relate to the interest payable on our 6.875% PEACS, as well as foreign-currency gains and