Adwords clients using Google Analytics to track the performance of their campaigns will need to link those two accounts before March 4, 2009. This update will require that your AdWords and Analytics accounts are linked and that you have "Apply Cost Data" selected.
To link those accounts and apply cost data, sign into your AdWords account and select the Analytics tab. (If no analytics data appears, then the accounts are not actually linked. Google has provided a handy video on how to do this here.) Once connected, visit the overview page and select an analytics account to display all profiles for the account. Select the profile you wish to edit, and see if cost data is already applied. If not, click edit from the right hand corner of the Main Website Profile Information box, and select the checkbox that says "Apply Cost Data.' Then just click save to finish.
Note that advertisers can only link one Adwords account to one Analytics account.