I've been using XMonad in a dual-monitor setup since I started working at Google in January... haven't had any problems with it. My general (rough) impression from walking around the New York office is that about one fifth of engineers here are using XMonad.
Really? I have not seen one other person that uses it. I haven't even heard it discussed, and I asked around a lot when I started. I'm surprised we have never discussed this, actually :)
