Well, on my Macbook I run a dual boot Mac OS X 10.5.8 , and Windows 7 Professional (Through boot camp) (I get access through my colleges MSDNAA services to Windows 7 Pro, which actually from what I have been told by MSDNAA, is the final retail version, not a trial version. I also have an Unbuntu Virtual Machine for my Linux class
On my old crappy Compaq laptop which has 384 MB of Ram, and an 80 GB hard drive, I run Windows XP SP3, and Unbuntu 9.04 (Jaunty Jackalope) with the KDE (Kubuntu) interface installed alongside GNOME, Unbuntu has been given a 1 GB Swap file for good measure and runs like a dream even with all the advanced effects on. Oddly enough I seem to use Unbuntu more than Windows XP now, and I love it.