my expierence so far
so far, i've rooted 2.1, then flashed 2.2. using rsdlite, i moved .ini file to correct folder(overwrite current file there) close all programs, put phone into bootloader, connect phone via usb, open rsdlite, find .sbf file and open within rsdlite, hit run, when finished, the phone will continue to reboot or "loop" on the droid eye, key to this is go into recovery and wipe catch and do a factory reset. this will take a little bit to boot up but when i does, it will be just like when u first got the phone(assuming u bought the phone new)
i've just done all this in the last 10 min. to see if it does work and in fact it does. i'm using Windows Vista 32x Business edition.
again, do so AT YOUR OWN RISK.
i'm just verifying that this method to flash 2.2 and go back to 2.1 DOES WORK.