Fedora is fully supported, and has the same upgrade possibilities as redhat had. The little red ! or blue checkmark is still present in Fedora. I upgraded my home redhat 9.0 machine to FC1 about 2 months ago, and my work machine made the same trasition last week. The distro upgrade itself is fine, but you may run into issues with anything you installed that wasn't from redhat. The upgrade cost me mp3 support, my favortie text editor pico, and I've heard there are often 3rd party driver issues with printer, network cards, and any other toys, but I haven't dealt with that personally.
It goes well, and I suggest checking out the fedora forum here on the site, there are several great guides on what to do once you get fedora up, including getting mp3 support back into xmms.