2010 10-K: Part II In 2009, cash provided by financing activities was $25.3 million.  Proceeds from stock-option exercises totaled $16.4 million and  excess tax benefits related to stock-option exercises and vesting  of restricted stock units totaled $8.7 million. In 2009, cash provided  by financing activities decreased by $25.4 million, or 50.1%, com- pared with 2008, driven mostly by a $17.9 million decline in excess  tax benefits, and to a lesser extent by a $7.0 million decline in  proceeds from stock-option exercises. The decrease mainly reflects  a lower average stock price at the time the stock options were  exercised and a decrease in the number of options exercised. Employees exercised approximately 0.8 million, 1.4 million, and 2.4  million stock options in 2010, 2009, and 2008, respectively. The total  intrinsic value of options exercised during 2010, 2009, and 2008  was $31.4 million, $37.4 million, and $113.6 million, respectively. We invested a total of $281.9 million, less cash acquired, related  to acquisitions over the past three years. We describe these acqui- sitions, including purchase price and product offerings, in Note 7  of the Notes to our Consolidated Financial Statements. See Note 18 in the Notes to our Consolidated Financial Statements  for information on events subsequent to December 31, 2010. Our discussion and analysis of our financial condition and results  of operations are based on our Consolidated Financial Statements,  which have been prepared in accordance with GAAP. We discuss  our significant accounting policies in Note 3 of the Notes to our  Consolidated Financial Statements. The preparation of financial  statements in accordance with GAAP requires our management  team to make estimates and assumptions that affect the reported  amounts of assets, liabilities, revenue, expense, and related dis- closures included in our Consolidated Financial Statements. We evaluate our estimates on an ongoing basis. We base our esti- mates on historical experience and various other assumptions that  we believe are reasonable. Based on these assumptions and esti- mates, we make judgments about the carrying values of assets and Deferred revenue is the amount invoiced or collected in advance  for subscriptions, licenses, or services that has not yet been recog- nized as revenue. As of December 31, 2010, our deferred revenue  was $146.3 million. We expect to recognize this deferred revenue  in future periods as we fulfill our service obligations. The amount  of deferred revenue may increase or decrease primarily based on  the mix of contracted products and services and the volume of new  and renewal subscriptions. The timing of future revenue recognition  may change depending on the terms of the license agreements and  the timing of fulfilling our service obligations. We believe that the  estimate related to revenue recognition is a critical accounting  estimate, and to the extent that there are material differences  between our determination of deferred revenue and actual results,  our financial condition or results of operations may be affected. We make judgments at the beginning of an arrangement regarding  whether or not collection is probable. Probability of collection is  assessed on a case-by-case basis. We typically sell to institutional  customers with whom we have a history of successful collections. We make significant judgments related to revenue recognition,  including whether fees are fixed or determinable and whether the  collection of payment is probable. For contracts that combine mul- tiple products and services, we make judgments regarding the value  of each element in the arrangement based on selling prices of the  items when sold separately. Delivery of our products and services  is a prerequisite to the recognition of revenue. If arrangements  include an acceptance provision, we begin recognizing revenue upon  the receipt of customer acceptance. Much of our revenue comes from the sale of subscriptions or licenses  for print publications, software, and Internet-based products and  services. We recognize this revenue in equal amounts over the term  of the subscription or license, which generally ranges from one to  three years. We also provide analysis, consulting, retirement advice,  and other services. We recognize this revenue when the service is  provided or during the service obligation period defined in the contract. We believe the following critical accounting policies reflect the  significant judgments and estimates used in the preparation of our  Consolidated Financial Statements: liabilities that are not readily apparent from other sources. Our  actual results could vary from these estimates and assumptions. If  actual amounts are different from previous estimates, we include  revisions in our results of operations for the period in which the  actual amounts become known. Acquisitions Subsequent Events Application of Critical Accounting Policies and Estimates Revenue Recognition 92