My late reply:
McAfee has gotten MUCH better over the recent, oh, two years. I used it for a while from my ISP, however, I eventually switched back to Avast since Avast has a much more advanced extended configuration that I can go through and set up.
In my opinion:
If you are a skilled computer user who knows how to recognize "bad" websites ridden with viruses, and if you only download from trusted sources AND you have a program in your browser that shows you when a site has had bad user feedback, go ahead and skip out on Antivirus.
If you are a new computer user, or have been using them but you arent extremely skilled with them, for the sake of reducing possible problems that may occur with viruses, keep Antivirus installed on your computer.
I keep Antivirus installed and updated on my computer for two major reasons:
My extremely large email inbox, and the fact that I am often connected to the schools network, and I use their network resources.
Software such as Sandboxie and other virtualization only go so far. Viruses can jump that "wall" if they are well programmed to completely infect all of your memory, even if its partitioned memory, some viruses can "get through"
Be afraid, be very afraid.