the way i did my OTA and got root back is this: (simplified version)
- install unrevoked 3, and unrevoked forevor (s-off)
-wait for OTA message
- click install later
- reboot into recovery
- do nand backup
- find and download stock 2.1 recovery zip file
- find and download (to a different location) clockworks mod zip file
- place stock 2.1 recovery file on root of sd card
- reboot into hboot
- hboot will ask to install recovery update
- click yes
- reboot back to OS
- wait for OTA message
- click install now
- wait for 10-30 minutes while phone does OTA update
- place clockworksmod zip file onto root of sd card (overwriting/deleting the 2.1 stock zip file in the process)
- reboot into Hboot
- when asked allow hboot to update recovery again
- reboot phone
- uninstall any old super user program you had on your phone
- install this new one using the information on this link
[APP] Superuser 2.3.5 - Now on the Market [2010-08-28] - xda-developers
you should now have wonderful froyo with root !