Sessions reset. Blame askjeeves. ( ask.com )
Apparently the server has been losing time still, so what is happening is that the clock is reset at midnight, causing times in the sessions to not expire properly.
If your find that auto-login doesn't work, it should now work. In the future, to make sure auto-login works, make sure your web browser saves cookies.
If topics aren't being marked as "read" when you read them, then logout, clear the cookie for the forums and log back in. Not much else you can do.
If you have been participating in beta testing the new forums, please make sure you log out of that forum too when reseting the cookies.