= http://en.wikipedia.org/wiki/Cobra_effect
FYI, we've had this system at Twisted for a long time, and that hasn't really happened. When it was first introduced, I argued that it might lead people to review too much; then Glyph counterargued that that's a feature, not a bug. History's proven him right.
It could be that because it's an open source project, and most development on it is by volunteers, that that mechanic is less strong: it's not like people collect bonuses or anything because of their scores... Nor would I suggest that in any other context :)
Just make sure this is what you want.
Another comment that has been made here is that you shouldn't have giant monstro-tickets: they should be split up wherever possible. Clearly that's not possible in every case, but the point is that monstro-tickets aught to be the rare case.
Edit: Meaning, we don't sell software, but we need software to run our day to day.
: https://github.com/leereilly/github-high-scores/, also https://github.com/kans/highscores