Most of the servers appear to be running various releases of Fedora (file servers, backup servers, oracle servers, etc).
This is a problem; it sounds like whoever was in this position before wasn't keeping up with upgrades. Failing to do so can cause problems for you:
- Bugs that were fixed ages ago.
- incompatible versions of configuration files.
- Unpatched security vulns
- Really old software
The last point really highlights a tradeoff. For example, Mumble changed their network protocol and the newer clients don't support the old protocol. If you don't upgrade the server there's a chance your users will and become incompatible. In another example the Ubuntu Django packaging is dramatically out of date on 8.04. This is a feature not a bug, but I'm not particularly fond of it.
Fedora isn't a bad choice for servers, but you need to keep on the upgrade treadmill. CentOS / RHEL are options, but if you don't have an upgrade process it just delays the inevitable. Personally, I use Ubuntu, but we have a mix of Ubuntu, Debian and Redhat at work. I don't use Ubuntu LTS because at some point the package aging gets too much.