There is the "bounty" system[0]: you (or anyone else) can offer up some of your own reputation as a bonus for answering the question. (For example: this Haskell question[1], and this C/GCC question[2] have had no/poor answers for a while, and the bounties have prompted more/better answers.)

[0]: http://stackoverflow.com/privileges/set-bounties [1]: http://stackoverflow.com/questions/11060565/tying-the-knot-w... [2]: http://stackoverflow.com/questions/11015672/gcc-removes-inli...