This excerpt taken from the NKE 10-K filed Jul 27, 2009.
Property, Plant and Equipment and Definite-Lived Assets
Property, plant and equipment, including buildings, equipment, and computer hardware and software are recorded at cost (including, in some cases, the cost of internal labor) and are depreciated over the estimated useful life. Changes in circumstances (such as technological advances or changes to our business operations) can result in differences between the actual and estimated useful lives. In those cases where we determine that the useful life of a long-lived asset should be shortened, we increase depreciation expense over the remaining useful life to depreciate the assets net book value to its salvage value.
We review the carrying value of long-lived assets or asset groups to be used in operations whenever events or changes in circumstances indicate that the carrying amount of the assets might not be recoverable. Factors that would necessitate an impairment assessment include a significant adverse change in the extent or manner in which an asset is used, a significant adverse change in legal factors or the business climate that could affect the value of the asset, or a significant decline in the observable market value of an asset, among others. If such facts indicate a potential impairment, we would assess the recoverability of an asset group by determining if the carrying value of the asset group exceeds the sum of the projected undiscounted cash flows expected to result from the use and eventual disposition of the assets over the remaining economic life of the primary asset in the asset group. If the recoverability test indicates that the carrying value of the asset group is not recoverable, we will estimate the fair value of the asset group using appropriate valuation methodologies which would typically include an estimate of discounted cash flows. Any impairment would be measured as the difference between the asset groups carrying amount and its estimated fair value.