QUOTE (MeeksDigital @ October 5 2008, 08:22 PM)

They were
sued over the number of colors the monitors can display... in the 20" model's case it was significantly less than most normal LCD monitors, and a lot of people have had a hard time calibrating the 20" models accurately from what I've heard.
I don't know the exact differences between the 20" and 24" displays, but the 20" are not up to par and the 24" screens are far superior.
Is there an Apple store, or any place near you that would have models of both the 20" and the 24" out. Check out the differences between them. Look at all angles. In the 20", form what I could tell, you can see brightness shifts as you change your angle, and it is not uniform throughout the entire hight of the screen. This to me is a show stopper for the 20".
Now, if at an apple store, also check out the cinema displays. Since price is an issue you probably aren't thinking this, but one option would be to pick up the 20" now, knowing its limitations and dealing with it, then adding a cinema display later on and use that as the primary monitor for photos and keep your controls/thumbnails on the built in monitor.
Since there are people reporting that they are happy with the 20", maybe it's enough to get you by until you can save up for a second. Go to the store and check them out, and if you can't notice a difference, then there must not be one as far as you are concerned.