I just now replace the stock 8GB for a Transcend 16GB Class 6 MicroSD card:
1. Connected EVO to USB, selected Disk mode
2. Copied contents of drive to temporary folder on PC
3. Powered-off EVO, swapped MicroSD cards
4. Powered-on
5. Immediately went to Menu, Settings, SD & phone storage, Unmounted then Formatted
6. Reconnected USB and copied files back to card
7. Powered-down and Rebooted EVO
I checked a number of applications I previously moved to the SD card and they run fine. I can now record 720p video without delays!!