Often you see two posters going at it inside a thread and neither will give in. However it's usually obvious to the people reading that one is coming up with the better arguments and the other is replying to try and get the last word in to save face or is simply just trolling.
I'd like to see a post mortem poll option for who won the argument in a thread and put their points across the best after a thread has died down or even while the thread is in progress.