The biggest difference, in my opinion, is the way packages are distributed. Ubuntu uses apt/synaptic and fedora uses yum. Both are great distros, I used fedora first. However, the community support is better in Ubuntu and if you are downloading the distro, you only need to download one CD for Ubuntu. It's four or five for Fedora. The major release upgrades are also easier with Ubuntu. Again it's my opinion only but I would say Ubuntu is more user friendly and Fedora is a little more bleeding edge.