I recently downgraded from 3.0. It went ok after I figured it out, but now when I want to just restore my iPhone, it wont let me. I keep getting error 1013, then it goes into recovery mode. What the eff?
Because of the baseband upgrade that 3.0 gave you I think. That's non-reversible for now I think. That's why the iRecovery / Quickpwn steps were required in the downgrade process.
I found (on a Mac) that when I tried to skip the very last step in the Gizmodo downgrade guide (the Quickpwn portion) I could get 2.2.1 onto the phone and sync with iTunes etc, but as soon as I tried to reboot the phone it was stuck in restore mode.
Going through the Quickpwn part of things got past that issue for me ...