I think the answer is "yes," especially when it comes to operating systems, but after reading some information on a Gizmodo post, I'm not so sure:
. . . if you have one of the Home editions of Vista, you can still run it on
Parallels on the Mac, but you'll be doing that illegally, violating
your End User License Agreement (EULA). Anyway, you can still legally
run any Windows Vista edition in Boot Camp on Mac OS X, but that will
require a reboot, and you can't use both Vista and OS X at the same
Why should Microsoft care if you run their software on Parallels? Why doesn't Microsoft care if you run their software on Boot Camp? Obviously this is an attempt to force you into purchasing the Ultimate or Enterprise edition of Vista, which costs more, but can that be the only reason?
I'll just stick with OSX and run XP on Parallels until it isn't feasible to do so any more.