You've been out of the loop recently. ACD series just does not cover Adobe RGB color space range all that well. Dell, NEC, and others (their higher-end series not the low-end garbage) have larger color space, nearing or even eclipsing Adobe RGB color space. As for the color rendition, calibrate. Calibrate both and Dell will be as accurate as ACD.
Let's face it. ACD was once state-of-the-art, but performance wise, it has been eclipsed by newer generation of monitors. For many, the difference won't be as noticed as ACD's prettier physical design and I happen to be one of them. But it's time that ACD gets more proper, full update.
While I agree that newer monitors offers a little bit more wider gamut of colors but I'm talking about quality not quantity, for example just because the new dell 2408WFP has a higher contrast/brightness doesnt mean its "better" when the colors are not as accurate when even professionally calibrated as to a 23"/30" ACD. But professionally the colors are more accurate on the ACD when both calibrating the colors properly on each monitors. You have to take account of the quality of the components inside that runs/processes the lcd.
You can take the same lcd that Eizo uses and use cheaper circuitry/chip/backlighting/glass and how backlighting is implemented/installed and end up with a worse monitor.
Just to give you an example with both Dell 30"and Apple 30" with the same lcd panel yet different components inside that drives the lcd and I know this is a bit outdated but still fair dell 30" and Apple 30" (and today 2008 I'm sure they both got modest updates as well):
http://reviews.cnet.com/4520-10442_7-6470175-7.html?tag=btn
quote from the site:
"Apple trumped the Dell in our DVD-playback test, displaying less digital noise and more-realistic skin tones, and it won the more technical rounds, with more-vivid colors and better grayscale differentiation. This is the monitor of choice, especially if you own an Apple computer, since the Apple OS provides additional configuration options."
And I know this is an apple support site but I found this real quick from just googling in just seconds:
http://discussions.apple.com/thread.jspa?threadID=1436508&tstart=0
This guy is talking about the 2408WFP and he saids:
"After having one of these monitors for a couple of days now i wish i had payed the extra and got an Apple display. After hardware colour calibration the colours looked good in Lightroom, but still over saturated in everything else. The brightness is just insane, i had to turn it right down as my eyeballs were getting fried.
I could live with all that, but the big problem for me is the 'sharpness' setting. It defaults to 50% and the only other settings are 0%-25%-50%-75%-100%. 50% is too much and causes fonts to have a halo effect around them and 25% is too little and fonts are blurred. It is at it's worst with black text on a white background. So reading this forum looks awful. I've tried all the settings on the 'font smoothing but that doesn't help."
But in the end he tweaked it to where he was able to read the forums without the headache.. but then the apple monitor is just so perfectly calibrated right out of the box and for professionals I'm sure even better to calibrate it with spyder2 or whatever your using.
The dell monitors are not horrible and if your not a graphics designer or anything to do with graphics its more than good enough for use but for me around that range to pay for an external monitor I'd buy the apple cinema display 23" or the 30" in a heartbeat.
And I'd do it again if I needed another external monitor for use (and I have and got myself a 20" ACD just a few days ago and its very nice.. I went to best buy to look at all the samsung/lg/hp/gateway/dell and just tweaking it for 2 hours at best buy.. they all dont look as good and at the mall I saw the dell 2408WFP and played around with it for an hour and was a nice monitor.. but the colors.. just look way too oversaturated on some colors such as red and some other colors not as saturated and didnt have that vivid/pop natural colors. I tried tweaking it for an hour and I couldnt get near of what I wanted and annoyed the dell stand guy. =D
Just comparing the 24" 2407WFP I had to the 23" ACD.. the 23" ACD just overall looks better in color rendition/realistic/web surfing, and just looks that much natural without it being overly bright or overly saturated and "just right." I use the 23" ACD with its brightness only at 4-6 notches out of the whole 16 and thats still more than bright enough for me and when I'm in the darkness I use it maybe even 2-3 notches. I know someone who uses it at 1 notch.
IMHO, I think dell monitors arent all bad and some uses the same S-IPS lcds but the way its built/circuitry/chip/glass that it uses is not on par with Apple/Eizos. Thats where you see the big difference. I notice the glass on the ACD makes a huge difference as well as to the dell. When I look at the dell or samsung or LG monitors just the feel and look of the glass is a cheaper material and it to me the glass is important because the better the glass the better colors from the lcd will show through the glass (and of course accounting to the circuitry that drives the lcd as well has to be better too)... every little components takes account into making a good display and Apple has done a great job.
Final note: I also remember few years back reading a tech article about Apple using the same components as Eizos to making the ACDs. And alot of people were saying that buying an apple monitor is the cheap way of getting an Eizo quality screen.