My main machine is a PIII@866 which runs XP. This one's up and running 24/7.
2 Compaq Armada (PIII@450) laptops, one running Redhat (Shrike) and one running SuSE 8.2 (testserver for webdevelopment). In the not so distant future I intend to move the XP machine to SuSE as well, not right now because I'd miss a few applications for which there are no Linux alternatives.