I once read an article online about the "18 hour brisket". So, I stayed up one night and cooked one from about midnight till 6pm the next day. It looked like a chunk of coal at that point. And, it fell apart when "slicing", but it tasted fine!
I think Bludawg is right about pork butts - trust the bone. But, even though I know that, I still manage to get impatient. The other day, I was near the end of cooking a butt and I needed to move it just a bit to reach some other meat. The whole thing just felt "wiggly" like it was ready to fall apart. So, I took it off to rest. Well, it was NOT ready. When I started to pull it I gave the bone a tug - and it didn't want to come out easily. There were tender pieces - and some tough pieces. You just can't get impatient when smoking!