This system of empowering community members to endorse comments from newer users has worked really well on Gawker!
<< The editors are the only ones who can give you a star, and we'll be giving them out to the commenters we trust the most. ... [Y]our comments will automatically appear in the featured comments, and you will have the ability to promote non-star comments up to the top level. In fact, just replying to a comment will bump up to the front page. You'll also see all of the unapproved comments left by new users and can approve the ones that you think are up to snuff. But use your powers wisely. We're going to be taking a closer look at who's doing what. Use your star powers to make mischief, and we'll take them away. >>
<< The editors are the only ones who can give you a star, and we'll be giving them out to the commenters we trust the most. ... [Y]our comments will automatically appear in the featured comments, and you will have the ability to promote non-star comments up to the top level. In fact, just replying to a comment will bump up to the front page. You'll also see all of the unapproved comments left by new users and can approve the ones that you think are up to snuff. But use your powers wisely. We're going to be taking a closer look at who's doing what. Use your star powers to make mischief, and we'll take them away. >>
http://gawker.com/5311027/gawker-comments-are-made-of-stars