I'm using Mandriva The only wierdness is at the end of the install, you have to choose the video card manually. (normal VGA), and you can't test the settings of the video card or the installer borks. All the other hardware-autodetection works fine. After you install the video card works fine with X, I donno what makes it bork. Quite a few people are using ubuntu also, although I have not yet tried it. I believe that there are some x.org config fiiles to make ubuntu work with fullscreen floating around this forum.
I'm having a good time with OpenSUSE 10.1 in a Suse Linux VM. I had to follow the guidelines from the SUSE board on how to ensure that updates work via YAST -- it involved changing the locations of update files, but all in all it's okay. I'm also having problems switching resolutions -- at best all I can get is 800x600 but I believe there is a solution floating around here somewhere. If anyone knows the location of the Ubuntu 6.06 x.org config file changes, please post.
Scientific Linux is another good one My reason for running Linux was to run Linux-only applications that are officially supported on and/or precompiled for particular versions of Linux. Red Hat Enterprise is always one of the officially supported versions (if not the ONLY one), but costs money. Scientific Linux, which is a free-as-in-beer recompilation of Red Hat Enterprise, will theoretically run any third party software exactly like RHE would. So far, it has been running great on my MacBook Pro with Parallels. It is not the slimmest of distributions, but it is definitely full-featured and very easy to install.