Just got my Desire S, great phone, but the recorded vidoes (720p) wont play. Just black screen and sound. When connected to PC movie plays gr8 on the PC.
Here's my solution to the problem:
1. Switch phone off
2. Open phone
3. Remove battery and uSD-card
4. Re-insertt uSDcard and battery
5. Start phone
6. Voila, playback works
Note: Just switch off and on / restart phone will not work.