Due to a change in the 2.1 roms, they way the phone recognizes usb connections, (and by association the way devices recognize the phone as connected to usb has changed). When you try to connect the phone to your computer you are given different options. Now, you have to select the connection type from the notification bar. The default is set to "charge only." You might try setting the default to "disk mode" and seeing if that works. If not, you could try "HTC Sync" mode. Good Luck!

 

I had issues last night mounting my phone to my PC. Found I had to go into connect to PC settings and choose HTC Sync. Once I did that, and plugged my phone in, another menu came up and I chose mount as hard drive from there and everything worked