Whose reputations? Not users'. Instead, it's server admins and email advertisers. Do you understand this service?

From a January press release:

Alberto Mujica, President and CEO of Reputation Technologies, feels the support of groups like these furthers the development of a more secure internet: "The MIT Spam Conference will gather some of the smartest people to have thought about, and worked on, this problem. Their support is a good thing for all of us who depend on email as a communication medium."

The proceedings are available, but, bizarrely, only as an ISO image.

Alberto Mujica: Reputation Management for Email | MIT Spam Conference 2007