The 23" has 1920 x 1600 pixel resolution while the 20" has a 1650 x 1080 pixel resolution. The original 22" Cinema Display is 1600 x 1024 (I've got one and love it).
There is also some brightness & contrast ratio differences between the two, which you can find on the Apple website.
As for the rumors of the style updates, well so far they are just rumors. While I have no doubt that new ones are on their way (eventually), the current ones are still mighty nice.