Trident, the problem with viruses is that one infection is one too many.

You may not conciously visit any "dodgy" areas of the internet, but if one of your "safe" sites gets hijacked you won't know until you've been hit.

Also you can get still get viruses embedded in e-mails. Can you be sure that none of your e-mail contacts will ever become infected and send you an infected message?

Without a virus scanner you probably won't know until it is too late. I would strongly advise that you use something "just in case". The performance hit of AVG is so low you will hardly notice.