After switching from a G4 PowerBook to a new MacBook Pro (Tiger to Snow Leopard), I found that external projection displays were noticeably dimmer and off color.
I tried calibration with the ColorSync Utility (located in /Applications/Utilities) without success. I copied the VGA color profile over from the G4 (Version 2.0.0) and changed from the Snow Leopard color profile (Version 2.1.0) and the result was a major improvement in the projector image.
[crarko adds: I haven't tested this one. It's good to know the color profiles are compatible. If it's a projector you use frequently, creating a custom profile for it in ColorSync could also be useful.]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20100629123219886