I almost went for the 30in Cinema Display, but decided to go for the 24in iMac instead. The benefits of having another computer in addition to my Macbook Pro are great for so many logistical and practical reasons.
I think of it as a very reliable, stationary home base.
I have two identical 19” monitors side-by-side (after installing in my PC the required video card) so my screen view is aproximately 31” diagonally. I use it to view at work two or more programs simultaneously (email & database usually).