Just for a laugh I spent a couple of hours today installing SUSE 9.2 on my PowerBook. No, I'm not fed up with OSX, I just wanted to see how well VirtualPC handled it.
All in all, it went surprisingly well - although it took longer to install than WinXP !
I chose the Gnome rather than KDE variant as I prefer that desktop, and more importantly it include Evolution which is a three-quarters decent mail client.
Ultimately though it's pretty much a waste of effort. OSX already has all the good bits from Linux and quite a few very polished apps (and no need to resort to the command line to do anything clever !). And it's pretty slow (hey, it is running via an emulation layer after all). If I really needed Linux it would be better to sacrifice an old PC to the cause, but as all I'd really use it for is Apache/PHP/MySQL and MAMP does a really good job of that.