Unity destroys my PC if I try to run anything else with it. I accidentally clicked my DD link when I had World of Warcraft tabbed and Unity crashed, my browser crashed and WoW locked up for a good 10 minutes before I finally managed to force it closed with task manager (which didn't actually appear visible, I just had to guess at what I was doing with tab/spacebar). It might be a memory thing, since I only have 2 gigs of RAM, but it's a bit troubling since no other programs cause that kind of havoc with my PC and I was under the impression that Unity was lightweight to begin with (I mean my computer is fine tuned for gaming, there's absolutely no unnecessary processes or services running and it's even a fresh install of Win XP Pro).
On the bright side, everything seems to be fine once the game is actually loaded up. On the downside, that means these issues are probably inherent with the game engine.