* Move too quickly
* Too much to learn to quickly, each version has serious breakage from the previous. 
* I have to cary lots of custom packages, and rebuilding all of those for each new release is a pain. 
* Wrong runtimes. Moving to Ruby 2.0 really quickly and dropping previous Rubies, etc.
* Lots of commercial/third party applications are not available on Fedora. (The stuff you'd run on the servers in bigger companies often times).

In general, I love Fedora. I use it as kind of the what's next look ahead. But living in a server world, EL is what I need for stability.