Sorry, I haven't had a reason to go the Linux route for about 5 years.
This honestly surprises me, Ober. So you run your PHP sites on a Windows Server?
I have since ditched linux on the desktop, which I believe is ONLY good for development machines, in favor of a Mac. I don't think I'm going back. While there are things I miss about Ubuntu specifically the package management, Mac OS X make up for it in other ways, namely polish. It's just as good as an Ubuntu machine for Java and Ruby development.
Our servers are all linux. We mainly run Ubuntu, and we have since 2006. Before that we were primarily Debian. We have two CentOS boxes in our staging environment since we sometimes have to support our software on RHEL and CentOS. Ubuntu is the clear winner for us, and as of now we wouldn't consider anything else. It's perfect for our application. I honestly haven't thought about OS on our servers in years. Ubuntu is usually a given, the only option.
BTW the reason we've never considered Fedora: They don't provide a clean upgrade path between releases. You have to reinstall the system. The Ubuntu release schedules make sense, and there is a clean upgrade path between releases. Ubuntu also has a lot more packages available