My authority comes from reading a lot of Linux-related articles, not from using Fedora. I have used Ubuntu and Xubuntu though.
First of all, Fedora is definitely free for everybody to use. It is more at the forefront of including new technologies, for the fun of playing with them and to give them some audience so they can be tested. Think PulseAudio (which broke audio for a lot of people – Ubuntu’s done that too though), PackageKit (a new unified package manager, can’t recall major problems with that). So a slightly higher risk of a broken system but with newer developments to play with.
Ubuntu has a larger community though, and when somebody developers some software that runs on Linux, an installer for Ubuntu is most likely to be available because it’s more popular. Oh, and it can ship CD’s to you for free even if you don’t really need it ;-)