Tim:
Brute force and ignorance is a tried and tested method. Trying to be clever with boot menus, and carefully selecting specific partitions while installing, often goes awry. Not to mention the times you come across an installer that only wants to do a full takeover of your install drive and nuke everything that was on it.
Joe Zeff:
In all the years I've been doing this I've never had it fail with a Fedora re-installation. Of course, I always have a full backup of /home before I upgrade or re-install, JIK.
Me neither, but better safe than sorry.
I hate having to deal with back-ups, it's time-consuming. Things can go wrong with them too, like what my web host did: Backed-up and restored my site's files without telling me (they were probably doing some maintenance on their gear the first time, the second time they were flailing around in the dark after they'd destroyed their perl installation). Every file had their permissions fouled up. Twice, now, I've had to un-munge about 1500 files.