As of mid September 2010, I finally found the first advertised DVI to Display Port adapters, so older Macs like mine can use the new display port Cinema Displays. Unfortunately, they are expensive ($150 for an adapter!), require USB power (they're an active device), bulky (they weigh 2 pounds), but the one total killer is that none support higher than 1920x1200 resolution, which on the 27" monitor must be further reduced to just 1280x720 to fit the aspect ratio.
Guess I'll have to roll the dice and buy a Dell monitor for my 17" Macbook Pro. What was the first year that Macbook Pro's even came with a display port? Wasn't it 2010 models?
You might want to look at AT-DP400 which is a dual link DVI to Mini DisplayPort Converter, which does support iMac's highest resolution of 2560x1440.