Distro, Applications and LearningI've used quite a few Linux distributions and have the following recommendations.
If you are using Linux just for play, I would recommend MEPIS. It's very easy to install, and is based on Debian, for which there is an enormous community and lots of software to try out.
If you are doing a little work and a little play, you might try out Fedora Core. It's basically a community version of Redhat. It's very big and has a big community. Further, many commercial packages run fine on it.
If you are doing mostly work, I recommend Suse. There are some packages that require one of the "big" commerical distributions, and will basically only install on RetHat Enterprise or Suse. For example, I do a lot of development and Oracle would only install on Suse for me. Suse costs money, though you do get some decent support for your dollar. It was easily worth it to me.
Other software I would recommend:
Groupware: I really wanted to use Evoloution for my groupware, but it was fairly unstable and has very primitive HTML capaibilities, which meant my corporate standard email signature would not work. Also, it would just "stop working" from time to time. I moved over to Thunderbird and it is much more stable for me. The down side is that it does not have an integrated calendar, et al, yet (though they're working on pieces). I think if Evolution incorporated the Mozilla layout engine, I'd move back.
Office Suite: OpenOffice of course.
Desktop: KDE looks nicer, is more polished and more configurable, imo. I went with GNOME, though, because certain "core" programs for me were GTK apps (e.g., OpenOffice, Firefox, Thunderbird). A lot of people don't care about this, so you may want to try out both. Most distributions will ask you at installation which you would like to use, and it might be a lot of fun to switch back and forth for a while.
As far as learning, I would personally take the following approach: Install Linux and do you stuff, whatever your stuff is. Gaming? Do gaming. Programming? Do programming. Graphics? Do graphics. Learn Linux in the course of doing your stuff.
Linux is pretty great. Have fun and be productive.