It's worse at a business.
After we got hit with the blaster worm, we ended up going dept to dept - PC to PC and ran a virus scan on every PC along with Adaware and spybot.
The amount of things we found were amazing. Well, at least to management. The help desk people have known all along users were downloading Bonzi buddy (shudder), KaZaa, AIM, Weatherbug and more.
I had a few users ask me during this "Why do I get so much junk mail?" and then I do a scan to find 10 different ad programs, real player and two messengers.
I look at it this way; stupid users=job security.