I've had all those too and there is no way that the MBP wins. Yes, if you're looking from a distance with a varied desktop pattern it might look similar to the cinema display. BUT, if you are actually WORKING on the computer and need color accuracy, lack of shimmering grain, even illumination and good viewing angles, the MBP will without any doubt lose to both the powerbook 15" (not 12") and cinema display. Yes, the powerbook is less bright, but I bet you it has relatively even illumination and accurate colors and is capable of showing gradients...
Unfortunately, photos can't capture these things...
Bingo.
I concede that ALL lcds will exhibit some form of grain. That's the way it is. But on a 20" you are naturally not sitting 1-2 feet away from it. On the other hand most users of a MBP will have their screens positioned a foot or so from it.
Herein comes the trouble, the granularity of the 15" panel on the MBPs is more discernable at its usual viewing distance than the ACD.
Edit:
Hell, in fact post the pictures. On my colour calibrated desktop LCD my whites have a clean white hue, but on my MBP that is calibrated to the same colour temperature all I get is an orangish-reddish tint with my whites. The MBP screen wins an ACD? Even if it suck I doubt it would suck that bad.
If you are using your displays without any form of colour calibration you are not even fit to talk anything about quality.