How to Upgrade Unofficial iPhone 2.0 Firmware to Official 2.0 Firmware

Macrumors has a useful post on how you can upgrade (downgrade, technically) from the leaked "iPhone1,2" firmware to the official "iPhone1,1" firmware issued early this morning. The leaked firmware was intended to only for use with iPhone 3G before it got out to the masses. In short, you need to download the correct firmware, and hold down the option key when you check for firmware updates in iTunes, allowing you to pick the file you want to install. [Macrumors]