* Lots of dropped calls. This might force me to try and downgrade back to Mobile 5.
* Less battery life. I used to get 3-4 days on a charge, but now get only 2-3.
* All the organizer apps (Task List, Calendar, etc.) are much better.
* On a related note, the new Google Maps Mobile has a new feature where it determines your location based on cell tower presence. Since my phone does not have GPS, this is very nice.