I would however love to be able to bump up a post of my choice to the front page for every, say, 1000 karma points earned. Let it have above normal gravity (i.e. make it sink quicker), but a chance to promote a single post once in a while would be genuienly cool.
Edit - to clarify, I don't mean that 5000 karma will give 5 boosts. Just one. You use it, you then wait for another 1000 points to get this perk reinstated. Or even start raising the cost with each boost - 1k, 2k, 5k, etc.