I think thats all happened to us all at some point or another.
Something that may be worth mentioning for those new to tournament poker:
When a player is knocked out then you get one step closer to the money, leaving them with some chips means someone else still in who can beat you. If your not going to beat the guy all in bluffing
at the pot knocking the winning hand out to win a small side pot usually isn't worth doing. Best off just checking it down.
Of course I would disagree if there is a somewhat sizeable sidepot up for grabs.
The situation described by Hesh though, there was no side pot so all that was acheived by the bet was to let the all in guy survive. The better didn't win anything in this case.
Its fairly normal for a bet in this situation to push out the other players, so betting to create a sidepot really has no merit at all.
Its a lesson we should all learn, so take this one aboard ;]