With the release of Fedora 13 about a week ago, I decided that my Fedora 11 workstation was getting a little long in the tooth and was due for an upgrade (not to mention the fact that Fedora 11 will go End-Of-Life [EOL] in about 2 weeks.).
I have a separate /home parition so I wasn't too worried about losing stuff, but I opted for an upgrade instead of a clean install. I backed up /etc just in case and dropped to runlevel 3 and ran the preupgrade-cli client that Fedora provides for upgrading. That process ran smoothly and it prompted me to reboot to being the upgrade.