The 20" panels are 8 bit vargz. Check the Dell website and wait for a "special". They happen pretty regularly - every other week or so, it would seem.
macmate, I thoroughly agree with you that there is much more to picture quality than just the panel. But your comment said "the apples have a much better panel." I was simply pointing out that the panels are the same for the 20" wide models.
For colour critical work you'll want a very good crt.

You can calibrate the dell or have it calibrated for you. There's $400 difference during the very regular dell specials, it is a significant mark-up for many, and given the drop in panel costs, i believe the original poster is right to note that Apple are lagging in their price policy.
I have both screens sitting on my desk and in my opinion only there is very little to choose from in output quality when you have properly adjusted and calibrated each. There were many reports on early batches of the dell that there were some significant display issues, but these do not seem to have been a problem for quite some time. Others may think otherwise. Perhaps you should go and have a look at them using some test images of your choice (if this is critical to you) before you decide.
As I said, I cannot comment on the difference between the Apple 23 and Dell 24 as I haven't seen them together. In the end designershub it is your choice.