My trackpad cannot register "hard" clicks now after the 10.6.4 update. I can use the touch-sensitive trackpad functions without depressing the pad, but that limits my usage. For some apps, I want to press down the pad, instead of tapping it lightly. I have to press it down several times just to get it to respond. I think the culprit here is the 10.6.4 update or the update to the trackpad.
I recently erased my hard drive and installed 10.6.1. With 10.6.1, it was still working fine. The problem with the trackpad started when I updated to 10.6.4.