Originally Posted by matttye

Backup your internal sd card by mounting the phone as a drive on your computer and copy/pasting everything over.

External sd card shouldn't be touched, but you might want to remove and/or back it up just in case.

As long as you have a google account, when you come back after a factory reset it will restore your contacts, wifi networks, calendars, mail, apps, pictures from Picasa etc.

It's pretty painless, it's mainly just having to reconfigure settings as you like them that's a bit annoying.