avast! On Mac? To install or not to install...

[Randy B. Singer]

okay this is an interesting read, sorry to jump in with another question, what sort of detrumental effects would running an AV have?

This article is a few years old, and somewhat outdated, but the concept is still valid:

Mac OS X anti-virus software: More trouble than it's worth? | MacFixIt
Mac OS X anti-virus software: More trouble than it's worth? | MacFixIt - CNET Reviews

I hear from folks who are suffering from nasty software conflicts caused by AV software all the time. Yet when I ask them how many pieces of malware their AV software has saved them from (noting that Windows viruses and other things that don't run on the Mac don't count), I've yet to hear anyone tell me that it has saved them from anything.

I'd recommend that Mac users interested in the topic of Macintosh malware have a look at:

Macintosh Malware Guide
Thomas' Tech Corner » Mac Malware Guide
(which is written by someone whom I trust, as he is an actual Mac user, he isn't trying to sell AV software, and he isn't in the "security field")

There is an associated comprehensive list of all of the malware for Mac OS X, which is kept meticulously updated, here:
Thomas' Corner : Mac Malware Guide
On the far left of this list each piece of malware is rated for its
"threat level."
You can use this malware catalog to determine for yourself what the threat to your Macintosh is.