I'm running Win 7 via Bootcamp only because I have a need to run Outlook for work. Everything else I've found a Mac application for. Believe me I would really like to find an Outlook equivalent but have not so far. Also I have 3,200 contacts, to deal with. To the topic: I would _never_ run an antivirus app on the Mac side, its just not needed. Fear based selling has gotten out of control. There is no need for AV apps on a Mac.
I'm running Win 7 via Bootcamp only because I have a need to run Outlook for work.