assumptions about expected future operating performance, such as revenue growth rates, operating margins, risk-adjusted discount rates, and future economic and market conditions. Our estimates of discounted cash flows may differ from actual cash flows due to, among other things, economic conditions, changes to our business model or changes in operating performance. Additionally, certain estimates of discounted cash flows involve businesses with limited financial history and developing revenue models, which increases the risk of differences between the projected and actual performance. The long-term financial forecasts that we utilize represent the best estimate that we have at this time and we believe that its underlying assumptions are reasonable. Significant differences between our estimates and actual cash flows could materially affect our future financial results, which could impact our future estimates of the fair value of some or all of our reporting units.  Determining the fair value of our reporting units also requires us to use judgment in the selection of appropriate market comparables, if there are any, and the amount of weight to ascribe to fair value measurements that are based on the market approach.



Any significant reductions in the actual amount of cash flows realized by our reporting units, reductions in the value of market comparables, or reductions in our market capitalization could impact future estimates of the fair value of our reporting units. Such events could ultimately result in a charge to our earnings in future periods due to the potential for a write-down of the goodwill associated with some or all of our reporting units.



    Cash Equivalents and Marketable Securities

          

    Cash equivalents consist of financial instruments which are readily convertible into cash and have original maturities of three months or less at the time of acquisition.  Marketable securities consist primarily of highly liquid investments with maturities of greater than three months when purchased.  We generally classify our marketable securities at the date of acquisition as available- for- sale.  These securities are reported at fair value with the related unrealized gains and losses included in accumulated other comprehensive income (loss), a component of stockholder’s equity, net of tax.  Any unrealized losses which are considered to be other-than-temporary impairments are recorded in the other income (expense) section of our consolidated statements of operations.  Realized gains (losses) on the sale of marketable securities are determined using the specific-identification method and recorded in the other income (expense) section of our consolidated statements of operations. Please refer to Note 18 of the Notes to the Consolidated Financial Statements in Part IV, Item 15 of this Form 10-K. We measure our cash equivalents and marketable securities at fair value. The fair values of our financial assets and liabilities are determined using quoted market prices of identical assets or quoted market prices of similar assets from active markets. Level 1 valuations are obtained from real-time quotes for transactions in active