Particularly in this forum it is severely needed. 
I'd like for the starter of a thread to have the ability to block individuals from posting in his thread, although I can see the obvious opportunities for abuse (squelching of opposing opinions, etc.).
We seem to have a couple of

's who insist on hijacking practically every thread in sight. Funny comments are one thing, but 15-20 off topic posts in a row can seriously derail a thread.