I'm not the best person to ask this question of, but my own feeling is role
based. I think that you need it for file sharing machines--to prevent
spread of bugs that replicate via file shares. That said, I haven't always
had it in place. I do like the corporate antivirus products that let you
protect both the server and the clients with some centralized monitoring
ability, and pretty reasonable per-seat costs.
It is a two-edged sword, though--a false positive can down the server or
some significant line of business app.
