I just discovered that you have to fiddle with a Dell display to get it to look right on a Mac.
After my main editing system died last week in the middle of a project (long story), I had to quickly switch and finish the project on my macbook. It was a 720P project on an external hard drive, so this was no problem.
So I unplugged one of my Dell 24" displays from the dead computer, and set it up as a secondary monitor for the macbook. What I noticed through this process was that the footage looked way brighter on the macbook screen than it did on the Dell screen.
I went fiddling in the physical menu of the monitor, and what I discovere was a setting on the monitor menu that changed everything!
Open the menu, and use the buttons to go over to "Color Settings". Next to "Color Settings Mode", you'll see PC Mode and MAC Mode. The interface sucks here... light blue means selected, and bright white means unselected. So unbeknownst to me, I had been in PC Mode for a whole year! I switched to Mac Mode, and all of a sudden, the screen colours brightened up and matched the macbook perfectly.
BTW: I highly recommend Dell 24" displays. They are reasonably priced, and absolutely comparable in quality to the 23" Apple Cinema displays. I like them better because they are a bit bigger, a lot more adjustable, and have a black frame instead of silver.