I think something like the "thanks" feature would be a great way to eliminate the great number of "thanks" and "me too" posts that sometimes take up a lot of threads.
If you want to know what I'm talking about:
[ame="http://www.vbulletin.org/forum/showthread.php?t=122944"][AJAX] Post Thank You Hack - vBulletin.org Forum[/ame]
I think it's compatible with all vbulletin versions up to v.4 as far as I can tell.
There's also a "thumbs up/thumbs down" feature which does basically the same thing too.
