I think it would make sense to update the monitors when Apple updates the desktops. I expect that Apple could either do a press release and update them within a few weeks if there is nothing but hardware upgrades to the Mini, the iMac, and the Mac Pro. Apple was waiting on some Intel quad core chips being released this month. OR, if there are model changes, then could be anytime between now and first week of March. I would assume we will see a 20" and a 30" to go with the new 24," but maybe they will surprise us with a new size closer to 34" 36." Clearly, a lot of people want big displays, and I think the market is there for a bigger display than even the 30."
That's my guess.