I have a 27" main display I've used for 3 years by itself. I'm pretty good with 1920x1200 resolution and utilizing it, but some things are better with 2 monitors.
I now have a 2nd 24" 1920x1200 IPS monitor set to arrive today. My setup is quite interesting:
My computer room is the next room over from my bedroom. So what I did was drill a hole in the wall to run internet to all my gaming systems set up in my bedroom (I have a projector in the bedroom & 55" LCD tv). I then just recently got the genius idea to use my receiver to run my desktop to my projector through the wall, and use a wireless keyboard and mouse in my bedroom when I want to use the projector.
And then I got more genius.
This 2nd monitor's input will be decided by the receiver. I can flip on Xbox, PS3 or use the monitor to extend my display. The way I routed the cabling I can play the sound from my Xbox / PS3 on my computer speakers simply by plugging it into the extended headphone wire I also ran through the wall.
So now I can do console gaming on my 2nd monitor, or flip it and use it for real estate on my PC, all while my 27" is dedicated to my main PC display. It basically works like this:
Xbox/PS3/Secondary PC output -> Receiver -> 2nd monitor
I just flip the receiver to whichever I want to use, and it is all operated in the other room. So when I play xbox for example I don't even have to hear the system noise, and since the controller is natively wireless, I'm good to go. If the xbox controller (or PS3) starts to run low on battery, it can charge via a USB port on my computer.
So now I can basically run my PS3, Xbox, & PC to either a 55" TV, ~100" projector (1080p), or my 24" monitor that is arriving, and have the sound working in either room.