For the most part, AV is pretty unnecessary for Linux since it's built with security in mind. The main thing is making sure that one doesn't do anything stupid like executing untrusted binaries with root privileges etc. There are actually much worse possible ramifications behind all of that. Things like rootkits, trojan horse, and backdoors being created etc. Linux is pretty immune to viruses, but there are still many security ramification to be concerned about, in other words.
However, there is probably no harm (At least in theory. Although I am bit skeptical about companies like Norton and not entirely trusting of their agendas.) in wanting to run AV software. Probably couldn't hurt. I would stick with a well established open-source based one though. That's probably because I tend to be a bit leary of proprietary software in general (I find it hard to trust software that was created by companies with greed as their primary motivation and agenda, but that's just me.). One that I can think of, that seems to be a pretty good one for Linux, is Clamav. Nice thing about it is that it's licensed under the GPL.
It really isn't a bad idea to put clamav on your system as a measure to look out for your friends that are running Windows, and whom you exchange data with. Mainly, by you doing so, you're looking out for them more than for yourself. It's also a pretty good idea if you run a dual boot where you're also running some sort of Windows etc. But Linux itself, used in a responsible manner, isn't really threatenned by viruses for the most part. They just don't really survive in it's environment since it's not so premiscious in nature like OSes like Windows are.