Unless it's a new thread I've got a choice of
   1) Starting at the top and skipping down over everything I remember seeing before,
   2) Starting at the bottom and skipping up until I see something I don't remember seeing before.

What I'd find useful is a feature to start me at what was the bottom of the thread when I last looked at it. Trouble is it would need a cookie to be stored every time I open a thread, and I'd guess this ability would need to have been built in from the start. So I shan't ask for it.