I've been having a repeated problem with my AT&T Tilt. Suddenly my battery will just start dying in a matter of hours. Finally I notice that in ActiveSync my calendar just keeps syncing. There will be a message like "Syncing calendar entry 700, 701, 702, 703, etc. It just keep going and never stops (thus draining my battery). Also, during this time if I'm in an area that doesn't have 3G then all my calls where going straight to voice mail.
My first fix was to delete my partnership, recreate, and resync. That worked once but then I added a new appointment in Exchange (in Outlook not on my phone) and about 30 minutes later I had a message that my battery was almost dead. It was fully charged 30 minutes ago, so I checked and sure enough the calendar was syncing away. This time the delete and recreate of my partnership didn't work. These steps did.
It seems to be related to the DST changes but I'm not sure if it's a problem on the Exchange server or on the phone. Hope this helps.