It's my understanding that one should not mess with sharpness on lcd displays if they're hooked up via DCI cables. As far as I know adjusting sharpness is only necessary when using analogue cables (as are some other adjustments).
Either way I use DCI, and I've left mine at default and the sharpness is one of the best things about switching to lcd for me, I find it very easy to judge..
I use cleartype, on most fonts and sizes it works well for me, it can also be adjusted for more or less smoothing to taste.
Btw, does anyone else have issues playing video in full screen mode? For some reason I can play it fine in a window, but in full screen I get very strong jittering for no apparent reason.