Right now I am using 6 different OS to just test and learn on.
I setup a VM Ware workstation (Allows for virtual partitions to load multiple OSwithout reboot) which has the following OS on it:
-Win XP Pro: (Main OS)
-Win Longhorn: (Testing)
-RedHat 9
-Mandrake 10 Pre-Beta: (Testing)
-Windows 2003 Enterprise Ed
-Free BSD
I mostly use XP Pro for all my daily activities, nd have been testing the longhorn and mandrake 10 for release. I use the RH, 2003, and Free BSD for jsut playing around on and learning.