If you receive the "Action Required Cost Data Change" Email from Google it may seem a little confusing, I know I read it a couple times, and you only have until March 4th to make the required changes.
To help alleviate some confusion Google has an employee, Stephen, actively answering questions about the email; below is some of his answers:
First, some background:
Right now, Google Analytics will attribute clicks and impressions to AdWords as long as the visitor has the 'gclid' auto-tag in there request. This will happen regardless of what account the tag is related to. For example, if I create an ad in my AdWords account, and direct it toward your website, then you will see clicks attributed to my AdWords keywords in your Analytics account.
There are other consequences to this, but that is the most basic behavior a user might see, and we believe that it makes our advertiser's less secure than they should be.
The immediate consequence:
This change will prevent the auto-tagged keywords from being attributed to AdWords unless the AdWords and Analytics accounts are linked, or unless the Analytics account has had 'cost data' applied. So if I decide to make an AdWords ad for your website, then the visits I send will be attributed to the source 'Google Organic'.
What should you do?
It depends. While the change will effect all Analytics accounts, not all Analytics users want the same behavior in their accounts or have the same account structures. I think that's one of the things that makes it hard to explain this issue.
If you only have one AdWords account and one Analytics account, then all you need to do is make sure they're linked together. That's the first set of steps in the email we sent out.
If you already linked them, but chose not to 'implement cost data', then you'll need to follow the second set of steps above.
If you have multiple AdWords accounts that you track through one Analytics account, and you want AdWords visits to continue to show from all of them, then you you need to request that the data be linked by AdWords Support by using the 'Contact Us' link in your AdWords accounts. The full details are in the 'FAQ' link in the email, which you can also find here: http://www.google.com/support/analytics/bin/answer.py?answer=140391&utm_source=costdata&utm_medium=email&utm_campaign=en_us
You can visit the Google help center and read all responses here: http://www.google.com/support/forum/p/AdWords/thread?tid=2031d315a6a35703&hl=en