Last week I upgraded my laptop to the latest and greatest version of Linux, Kubuntu 8.04 (code-named the Hardy Heron; each new version of Ubuntu alphabetically increments an alliterative adjective and animal).
The only issue was that when resuming from hibernation, the screen resolution would change. I filed a bug report and asked a question on a Ubuntu support page. The response was pretty quick... if I had been checking my email! The simple fix was removing a package obsoleted by the new version of X Windows.
I'm not brave enough to try the new KDE (and, apparently, neither are the Kubuntu developers, it's still optional). KDE 3.5 with a few tweaks is just about perfect IMHO, and still leagues ahead of OS X or Vista, at least in terms of functionality. The screencap shows a feature that has yet to be built into other OS's, the ability to drag-n-drop with sftp:// locations, which I find vital for website management.
There's cool and useful features like this all over the place. It's a near perfect OS!