If' you've got a Firewire drive, I'd suggest copying your entire 10.1 install to it with Carbon Copy Cloner. That way, if your 10.2 install should go wrong for any reason, you can erase it and copy the install of 10.1 back from the firewire drive.
I suggest the "archive and install" option for upgrading to 10.2. It'll keep all your third-party apps, and all your users and user prefs. Worked great for me.
CV