I used to run Dual 20" for a couple years and recently upgraded to Dual 24" and like people have said, its night and day for doing anything from work to surfing and games ... at work I run Dual 22" as well ... It comes in handy as my 24" has HDMI inputs so I plug in my 360/PS3 on one screen and can play NHL11 while still surfing on the other (like I'm doing right now

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EDIT: 1 thing to mention is if you can keep identical monitors for the same size monitors, as its easier to adjust colour and lighting plus it keeps resolutions the same on each side (obviously for different sizes its not possible but I'd still keep the same brand if its possible)