Same here, even with a bit of P2P stuff on my netbook, i have no A.V and i don't have any virus troubles.
If i have to spend £500 on a white shiny laptop to make sure i dont get a virus (not strictly true though eh) then i think i'll just stick to my current machine and if neccesary format my windows P.C every 6-12months for a couple of hours and crack on that way