Ubuntu passes the J. Angelo Racoma test. Its easy enough to install, and it works well enough without the usual headaches you would usually imagine having when doing a fresh OS install on your machine.
Read the blog entry here
Best thing is that even if my machine wasnt too spiffy (its a Dothan class Celeron-M running at 1.5 GHz, with 512M of DDR1 RAM), it can still support all this eye candy without breaking a sweat. I dont think Windows Vista or even XP can do that. I tried installing some 3D cube type desktop managers on XP and I wasnt so impressed.