i love ubuntu. i'm several months new to linux, so i can't really effectively use the terminal or do under-the-hood sort of things, but ubuntu is really working out well. my main os is still windows (sadly, but its for the gaming), and i've tried many other linux distros, including linspire, debian, and fedora core, as well as messed around with knoppix.
i plan on setting up my own internet site using ubuntu on an old p III server. the only things ubuntu gives me trouble is getting matrox drivers, (though they aren't necessary) and running ubuntu livecd on a mac (just a side experiment).
with dapper drake coming out soon, ubuntu will be even cooler, with the compiz and xgl stuff.