when i first bought my mac pro i debated the same question. i ended up buying Dells 24" widescreen display and never looked back. ive owned ACDs and frankly they dont compare. to make things even better is the addition of the HDMI ports on the current generation of dell displays. not to knock on apple but frankly the ACD is almost 7 year old technology at this point. they havn't really changed a thing in way too long.
I wouldnt say 7 years, as the aluminum versions with S-IPS displays were introduced in June 2004 so its turning 4 years in June 2008. http://en.wikipedia.org/wiki/Apple_Cinema_Display
But they have gotten minor upgrade in 2006 for higher brightness just as the dell monitors has gotten minor updates as well. Not to mention dell monitors imho isnt updated in quite a bit since they are not using LED backlit technology yet + dell 24" screens use the inferior S-PVA panels that are only 6-bit (they trick you by telling you its an FCR 8-bit sometimes, unless you get lucky in the dell lotto and get an S-IPS panel but then the circuitry/backlight/chipset/build quality/glass is inferior as the ACD's use same components as Eizos do).
I believe the apple cinema displays are the best in the lcd market for price for S-IPS panels but people have the impression that Apple cinema displays are over priced because of its price just 3 years ago, when a 23" used to cost $1499 but now you can get one for $799 with student discount. Not to mention the 30" ACD used to be almost $4000 and now its only $1700. I've looked at some NEC which are a bit better than the 30" ACD's but not by much but cost $2499.