Recently, Google started rolling out Adsense integration with Google Analytics. [If you have not got your invitation, fill out this form and Google will update you in 24hrs, I got it that ways!]
So far so good. The problem occurred when I clicked on the invitation link –Integrate with Google Analytics-on my adsense home page. It prompted me to either create a free account or use the existing analytics account.

I use two Google Accounts, one for adsense and the other for Gmail, Analytics, Orkut etc. After clicking on continue, this is what it had to say

There was no link , no option there to link adsense with the other Google Analytics account. If you are facing a similar problem here is what you can do:
- Go to your Google Analytics Account.
- Click on Analytics Settings on the top left side.
- Scroll down on this page and click on User Manager.
- Click on Add user link given on right side.
- On the next page, enter your adsense email address.
- Make access type as Account Administrator. [For some unknown reasons the integration would not work for View Reports account type]
- Select all the website you want to grant access and move them to right hand side.
- Save changes.
- Now go to your adsense account home page and click on Integrate with Google Analytics. You will see a similar page as shown in image on the top.
- Click on continue and you will find all your website names populated there. Enjoy!