I always have an issue with my PP to b&w... my shots come out rather lack luster. I know you mentioned using ACR which I recently have been trying. I sometimes have issues with bumping up the black as the eye lids and the mouth get so dark. Also, I have a 40D and find that it constantly under exposes. Should I just go manual and adjust for this?
with the B&W's, try using the gradient map. click on image/adjustments/gradient map. you can tweak it from there but it does a better job then clicking the B&W button. Hope that helps