This is already being discussed here - http://forums.digitalpoint.com/showthread.php?t=1229867 It is best to do a little looking before posting a new thread that is already there.
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Hmmmm... I've already seen some vBulettin forums using some script, so when user writes thread title, it shows all threads with similar subject, so (s)he can see if it exists or not. I think it'd be interesting here.
Hmmmm that looks like a personal attack Yes that would be an excellent idea I have seen that being used at a few other vB forums