What do you want from your display?
For me, the most important aspect to consider when purchasing a display is its use. How will you use your display?
If you are creative professional like me, colour accuracy, even lighting, SWOP/ICS certification are THE MOST important consideration. Some, well financed people in this catagory might even look at even better spec-ed displays from Eizo and Lacie but they are in another category (price & spec). ACD are good displays suitable for professional work. If this is you, it is worth it. If not, only you can decide. However, neither have 24"+ models yet.
IF you do not need that sort of colour accuracy/even lighting, then your options are greatly increased. Some people determine their purchase by price, some by design, some by response time/speed, etc.,
If you are a domestic user (ie. used for word processing, email, games, etc.,), I would suggest non-Apple brands. There are many better options. If you need colour accuracy (ie. photographers, designers, video editor, etc.,) you really only have Eizo, Lacie, Apple (and a very few others) to choose from at the moment. I understand Samsung is planning to release a pro-line 30" with hardware colour calibrator built in.
As for the discussion about the Dell and Apple... I believe the panel is the same but the backlight and electronics inside is different... (only if colour accuracy is important). So the value comes from what you want to do with your display.