slg really hit the nail on the head here. the overjustification effect is well known and hints at how potentially dangerous this idea is to Reddit's future.

I see the point Sam's trying to make by doing this, but does Reddit have a contribution problem? Hardly! If millions of people contribute to make a site awesome voluntarily, for no greater reward than the attention of their peers (and a desire to build a great community), introducing a new incentive might very well alter the magic bit that makes Reddit so great.

What about directing this 10% towards philanthropic or political goals instead? So by contributing my time towards making Reddit better, I'd get that attention I want and help make the world a better place.

This could have a dramatic impact on reddit's raison d'être, making it a powerful (and defensible) power for good.