if you get into that kind of thing: One computer, three operating systems running simultaneously.
CentOS 5.4 and Solaris 10 running in Sun virtualboxes on top of Windows 2003 Server. Right here in my office :)
(Yes, I'm running as root. I just got done installing CentOS. Get over it.)
Reminds me of how when I built a machine last year, I realized after finishing the Windows install and filling the hard disk that I was going to dual boot Windows and Linux. Then I realized that dual booting is out. Now that we have multicore CPUs and 4GB or larger memory sizes, dual booting is obsolete. Virtual machines rule.