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Remember, "The Fedora Project is a collection of projects sponsored by Red Hat, and developed as a partnership between the open source community and Red Hat engineers."
This is where Red Hat goes crazy and test new stuff they want to implement in the future. You will find that releases like 3 and 6 are stable because these are the ones where RHEL is built upon. Other releases are more experimental and unstable.
If you are a sysadmin and you use Fedora for your work stations or servers, you are crazy. While some releases like FC3 are very stable, their life cycle is very short and updates and patches will soon stop coming. Use fedora at home, to play with. But if your are looking at long term, go for CentOS or Ubuntu.
Again, thanks to the Fedora folks for their hard work, while I use CentOS at work, most of the success of this distro is thanks to them (and Red Hat of course ... dah!!!)