Some people just don't seem to make the connection between size and resolution, but Peyote is doing an admirable job of trying to explain it.
It's like this: if you get a 30" TV (as in, the 1280X1024 resolution range screens from Gateway and the like), you will have EXACTLY the same useable workspace as the 17" Apple LCD I'm staring at right now. All the text and graphics will be much, much bigger, but the number of pixels on the screen, and thus the useable working area, will be exactly the same.
For normal people, who sit about arms' length from their monitor, this would be very distracting, since only part of the monitor would be within my field of view, and I'd spend four times the effort I currently do moving my head and eyes to scan around the monitor while I'm working. The alternative is to move the monitor twice as far away, which would work fine, although it'd then end up functionally looking no larger than a 17".
A monitor like this would be great in one of three cases:
1) You have very poor eyesight, and the large size helps you see better.
2) You play a lot of games or watch a lot of movies on your computer, and would rather have to work from farther away so that you can get the cool gaming/movieing experience for less money.
3) You want the monitor to double as a TV.
As for the Apple monitor, it's in an ENTIRELY different category. Yes, it's more expensive, and that money isn't for the physical size--you're paying for the RESOLUTION. This provides vastly more (four times) working area than a 17" monitor or one of those 30" TVs, which is exactly why they're worth the extra cash and hassle of having to get a new video card.
If giant size is all you're interested in for one of the reasons above, but you don't care about the inconvienence of the field of view issues and don't want the extra computer working area (resolution), then it'd be stupid to waste money on the Apple 30". If, however, you want more working space, you'd be far better off buying an Apple 20" or 23" monitor, which will give you far more useable area than a 30" TV at a similar price.
That's what I'll be buying--I don't use my monitor as a TV, so the resolution on the Apple 20" is far more valuable to me than a 30" screen that would be functionally smaller than the monitor I'm using now. Even if I could afford the 30" Apple, I'm not sure I'd get it, since the field of view is just too large to be useful in my work--23" is about as big as I'd go.