I like really really sharp photos.
Even with a prime lens, I seem to be able to do noticeably better with my 450D by manually focusing using live view at maximum zoom than by using auto focus (even with just the center focus point selected and aimed at the same high contrast region that I am looking at in live view). However this is a painstaking procedure that requires a tripod and a fair bit of time; not really suitable for capturing fleeting expressions on people's faces or rapidly moving children.
Unlike my old film camera, the 450D lacks a prismatic focusing screen, and my eyesight isn't good enough to do better than the autofocus through the viewfinder without one. How do others deal with focusing for candid portraits? Any tips?