My office runs a windows network and, as a result, I keep a Parallels version of XP on my Macs. I've recently, however, set up a VPN solution with the office PC that allows me to tunnel in without needing to bother with Parallels. This left the approximately 12 gigs of windows on my computer solely to run one legal related application. However, in the last six months I've actually booted that application on my Macs 2 times. I could have easily just run it remotely via VPN and with an ever shrinking hard drive, today I officially put a bullet in the head of the XP files on my Mac.
So there you have it. I have 12 gig more space, slightly less flexibility, and no regrets.