Google Operating System reports that Google is testing a feature for signing in using multiple accounts.
While the post itself has a screenshot (which you can see above), it does not include any instructions on how to enable this functionality. This is obviously a limited or closed-beta test; the question is just how limited it is.
This functionality is not just “useful” – it is often vital. I have one account tied into an AdWords account, another account tied into Analytics, and yet a third Apps account. Merging them is impossible, especially as long as Google Apps doesn’t support Reader. Having a way to sign into all three at the same time from the same browser would certainly make things less irritating.