Great question
Does anyone have any idea if apple is going to update the ACDs anytime soon? I've been waiting to buy an external monitor to go with my MBP -- looking for something in the 23-24" range, using mainly for photo editing. I've heard the ACDs are one of the best considering price but it's been a while since an update. Also thought they may add a built-in isight to complement my MBP and let me use ichat with the external monitor so i can close my notebook. But alas, conference after announcement, no word on new displays. Just curious to hear any rumors or should i just break down and get the current version.
I have been scouring these forums looking for this same information and there does not seem to be much at all out there. Unlike other products, e.g. iPhones, iPods, etc., most information on ACDs is more in the form of wish lists, not hard, cold rumors.
It's true that the ACDs have gone almost three years without an update and really need built in iSight now that the external one has been discontinued. They could also use HDMI support, too. And, in May, Steve said that all displays will be LED backlit "by the end of 2008".
Personally, I'm waiting for Leopard to get a new MBP and, like you, really want an ACD to complement it. Seems logical to me that

might be waiting until the launch of Leopard to update the displays as the perfect way to show off the new OS. But, if they are waiting to update until after there are LED panels in 23, 24 and 30 sizes, it might be a long time.
My personal strategy is to wait until October and Leopard and decide then. Of course, if Leopard is not released until October 31st, that is getting fairly close to MacWorld in January, another ACD update opportunity... To wait or not to wait...