I have the LED ACD. There are a couple important things to consider before you buy it. Are you okay with the glossy display? Many people are not. Are you okay with being locked into the mini displayport connection? Are you okay with paying a fairly large premium for the LED technology?
Um, really there isn't a large premium for the LED technology in this case. The 24" nec goes for over 1k and is not LED backlit, but I do believe they both use the same h-ips panels (not 100% sure on that). And IMO, the led acd offers a much nicer picture for movies, viewing photos, etc.
Really, most h-ips 24" monitors go for over 600 new, so there really isn't a huge premium at all in this case.
I think it's not just the size, but the resolution as well. At 2560X1600, the display can't be cheap, plus add in the fact that's it's an H-IPS display with LED backlighting, has features like the Magsafe, iSight, and speakers, and on top of that Apple's high profit margins, and you have one expensive display.
Look at last-gen: $899 for 23". $1799 for 30". $900 extra for 7".
When the ACD's first launched(the aluminum ones), the 23" costed $1999, and he 30" was $3299. So, $1300 for just 7".
Really, when people buy 30", it isn't for the extra 6 inches over a 24 inch display. They buy it because it has nearly double the pixels of a 24" display.