There's one major problem thats plagued the Apple 30" for many years. The thread has been locked because of it. Nobody knows how to fix it. Not even Apple. Applecare just tell people to reinstall OS X. It doesn't solve it. Nothing solves it, not even replacements.
http://discussions.apple.com/thread.jspa?threadID=221104&start=0&tstart=30
http://discussions.apple.com/thread.jspa?messageID=7025127
http://kupuk.com/2008/03/06/spurious-green-and-blue-pixels-from-mac-pro/
Green and blue dancing pixels so many has named it, but its actually DVI Noise.
You know I've heard of this as well.. it really made me think twice about the 30" ACD... but I've found a thread someone after googling about the 30" Dell having this issue as well with some users.. maybe its just the lcd panel that has this issue?? I'm actually considering just another 23" ACD just since it will be much cheaper as well..