Ok for "defaults write ..." but, really, I don't see any difference between the four font smoothing levels, I've a good sight and I'm sure that from the lowest to the maximum smooth level a difference must be visible.
I've tryed to change this setting on an iBook with a 14" at 1024, where single pixels are distinguible on the screen, so if there is no difference between two different smooth level I think it's a bug.
Anyone can confirm or negate this?