Three. (Sort of.) I have Windows and Mac systems side-by-side running Synergy, so it feels like one machine. Each machine is running on a 25.5" Samsung so that I can get a broad view of what I am doing. However, the downside of the big monitors (and limited budget) is that they are both TN panels, which is a no-go for design. So when I am pretending to be an artist, or doing color picking for websites I work on, I use a 19" Dell monitor (S-PVA) which actually produces colors accurately. The rest of the time it is hanging out in the corner on an Ergotron arm.
