You mean a tipping bot? It's been discussed several times, and I recently collected Pros and Cons from previous discussions in a new thread:
Tipping micropayments on Bitcointalk.
I don't expect it to be implemented though.
I don't like the whole idea of rewarding other ppl with Bitcoins. No one will ever reward other ppl with bitcoins just for good posts
That's not true, it happens, but not often. High fees don't allow for small tips.