Jason:
From what I've read and seen, at least a couple of years ago, some LCDs couldn't be properly calibrated because: (1) the brightness & contrast varied a great deal with the viewing angle, (2) the color wasn't very uniform across the screen, and/or (3) the color wasn't very uniform over time. All headaches when you're trying to calibrate to a precise standard.
But maybe someone else here can tell you if that's still true for very many LCDs. I'm still using a CRT (a LaCie electron 22, a year or two old, which was very highly regarded for photo processing at the time), so I'm not an expert on current events.
Lisa