I have a MBP17 2.4GHz C2D, 4GB Ram, and this game is a waste of money IMHO. I have played it a lot on PS2 so I know how it's supposed to be.
On my MBP17 with the GH3 1.1 update and all settings on the lowest (800x600 res, low graphics, and no crowd) the timing is constantly wavering. I can play through songs and still get 98% notes hit, but it's near impossible to get good scores or more than 3 star ratings because it's near impossible to get long note streaks. The game will jitter and a note is missed.
For me, it was money wasted and several nights of frustration.