Do a full DFU restore to 2.2.1, then update to 3.0 through iTunes, so nothing is left behind. Wait for a Jailbreak (QuickPwn would be easier) to be released by the Dev Team then pwn it.
On a side note, I'm not really sure about DFU restoring... I think DFU has been disabled in iTunes 8.2. The Dev Team are supposed to be releasing a fix in the next version of QuickPwn.
I think I'll be waiting this out, I don't want any of my favourite apps (App Store and Jailbreak) to not work on 3.0.
But never upgrade from a Jailbreak. Unless you want to loose 500mb+ of your storage.