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I use one 30" and two 20s in portrait mode sideways, which is nearly perfect for web development..

1600-1680 pixels in height are perfect for large sites or FTP programms.

But even with that much pixels, space is rare.
I even thought about having two 30s, but i don't like having the bezel in the mid when sitting direktly in front of them.
 
At work I have a 14" laptop and a 19" LCD next to it.

At home I just use the 24" iMac after going for years with two 18" LCD's on my PC. The 24 incher seems to be plenty big enough, especially when using Spaces.
 
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