Here's my contribution:
1. Trackpad isn't accurate enough to play Brickbreaker as well as with the trackball
2. T-Mobile UMA is unreliable. With my 8900 it was always reliable for downloads and mostly reliable for calls.
3. Micro SD card is hard to remove.
4. Google maps is slow to find satellites. This is probably more to do with T-Mobiles 3G interfering with cell tower location assistance.
All in all not big problems but still things I miss about my 8900