Good point there Halfnium... I to run multiple OS's... Linux RHEL5 currently as my base with VMware and Virtual Box (VMware license form work) Virtual Box just to test with several other Windows and *unix versions running at once. eSATA cards make it really nice can have a small drive dedicated to an OS to help with the IO issues. But you can do the same as you say, share source files, code DB etc.... and with an internal virtual network live testing is easy as well...
But your right, Opensource is here, it is a big part of the web world. CC currently has done a good job of bridging things though. There are very few good, well supported inexpensive commercial packages out there. CC has excelled in that arena.
If the big players would stop fighting each other for the next "my interpretation of the standard is right so buy my product in order to make the web work" the computer world would be a much better place...
--Mitch