Is Anti-Virus Software Worth the Hassle?

The question of anti-virus effectiveness recently came up in my office.  Personally, I have a difficult time defending the performance hit that AV software causes, and an even harder time justifying the cost.  

As a fun exercise, I thought it might be useful to look for an answer to the following question:

If no reliable antivirus software existed, how would you defend your network/systems?

We're currently looking at an AV free solution for our environment that I'll share once we're up and running. 

You can follow the conversation here:

http://www.reddit.com/r/sysadmin/comments/1der4p/antivirus_is_it_worth_it/