I've connected the Dell U3011 monitor to my MacBook Air via DisplayPort to MDP cable.
Everything is fine, and the screen looks good. But: The "OS X motions" are not as smooth as on the MacBook itself. Open up Dashboard, Launchpad, browsing through iTunes... it isn't smooth.
This is a test configuration and i'm planning to buy the new Mac Pros.
So: Could it be that the Intel HD graphics are too weak for this screen resolution? (2560 x 1600)? I hope that a Nvidia or ATI graphics card handle the monitor better...
I had the same "problem" with my MacMini (also Intel HD3000).
What could i do to "make it smooth"? Or have others the same problems?