also..
btw, here are a few hints based on the troubles i had...
1. do a backup before u install the new OS and then copy the backup folder to another location. (~/Library/Application Support/MobileSync/Backup)
2. Write down your UDID number (from iphone screen in itunes - click the line that says "Serial Number". It will be right above where it shows your phone number)
3. Register your phone as a dev device in the ADC portal, otherwise it wont reactivate when your now OS boots.
4. Uncheck "Open ITues when this IPhone is connected" on the iphone screen in itunes - this way you can restore your old backup before itunes tries to overwrite your old backup with a new one.