This of course is not something I would advocate, specially if you P2P, however, I'd like to hear arguments from both sides.
I personally run an anti-virus and a firewall behind a router WITH Peerguardian. I know I am well protected, or at least for the most part, with this setup.
I would feel, well, NAKED without a firewall, even with the router. I haven't had a single virus, attack or problem since my configuration has been setup this way. Also, can P2P with no problem. And you may remember I was previously "smacked" via email and threatened with permanent disconnection last year.
Looking forward to hearing your views. I remember one time this gentleman was sitting at my house (at that time he was helping me with a program or something some years ago) pissing and moaning about me having an anti-virus program on my machine that it was slowing it down and causing problems. He inserted whatever disc he brought with him in my machine and up popped a screen saying it contained a virus.
He asked me for a copy of my anti-virus before he left.
I don't remember if he had any when he scanned his, but I think he might have thought he had a MAC or something.....