I don't know. I find gittip's model mostly rewards popular coders.
Where as tip4commit, rewards are not influence by popularity. I do see how fluff pulls could drain the pool. One needs to ask: Is changing a typo worth $4 dollars? Is it worth my time to do it? Maybe I should just click that merge button.
In my opinion bountysource is the best reward system, as it gives context, popularity is a boon, and it shouldn't generate fluff.
Just my two cents.