I downgraded back to 3.2.2 from 4.2 GM a few hours ago. Re-jail broke and am doing fine. I uninstalled all traces of iTunes 10.1 beta 2 and installed iTunes 9.2 went into DFU mode running Tiny Umbrella and shift+restored (on Win7) to my 3.2.1 firmware and restored. The only glitch I ran into is iTunes 9.2 said at 1st it couldn't open because the .itl (iTunes Library file, I guess) was from a newer version. I just did a search for that file and deleted it and all went well from there.
I downgraded because I was having strange wifi problems. I've never had a single wifi problem before, not even with the betas, until 4.2 GM. I hope that's not the final version. That would suck.