I agree, I have Spybot-S&D and it found viruses and trojans that NAV missed. I know, NAV! BUT as mentioned already, once norton is on your computer it'll take a hard drive crash to get it off.
I too am really happy I don't need to setup different users on my computer. I know a few people who have the whole family on it and the computer spends more time down then running. Viruses don't seem to care about who's using the damn thing, they just wreak havoc on the whole system.