I think I have a copy of ClamXav... Yep, I found it!
Can't remember the last time I ran it, however. I depend on SpamSieve, Ghostery, Java blocking software and keeping up with Mac news sites. But most importantly, I usually install apps only from devs with their own website and occasionally The App Store. I
never download anything from C|net, softtronic, macUpdate, Softpedia, etc. I just don't trust many 'software collections' sites, anymore. And I can't remember clicking a link in an email..., I don't even allow third-party images to open in Mail.
Speaking of email, if you forward a message, it's probably kind to scan it, since it will most likely be going to a Windows user... I'm too lazy, so I just don't forward much stuff... to friends, anyway!
Then, there are the people who refuse to use the BCC: field and dump everyones addy into the TO: and/or CC: fields; so long email address.
I have had a few other AV apps installed, but they never ever found anything and the only thing I noticed was they slowed down the machine while they ran.