I would add-
Save a copy of your sounds folder, if you use custom sounds.
And your films folder, if you care about those.
The sounds folder is a big one for me, since I'm on 28K dial-up.  Replacing it is a LONG PAINFUL download.  
I'm actually better off to call a friend with highspeed, have him download it, drive an hour each way to pick up the disc or removable memory stick, come home, eat dinner, watch TV, take a nap, and then install it.  Much quicker than my dial-up.  No joke.
MtnMan