I've seen many people on the discussion boards who regularly make excellent contributions and I think there should be a way to recognise these people so that newcomers know they can trust them.
Therefore, I think Duolingo should implement a Kudos system. The number of Kudos you have could be displayed on your profile and whenever you post. To give someone Kudos, it could work similar to the upvote system, except have no downvote, you can only give someone Kudos once and you can only hand out one Kudos every 6 hours. This would prevent people just giving tons of Kudos to their friends.
I'd love to know what everyone thinks about this!
I'm a little wary of adding yet another scoring system to our coins, levels, lingots, vocab-counts, upvotes, streaks, leaderboard rankings, etc. ... if I might modify the suggestion: Slashdot (one of the most ancient and successful web communities) has a system called karma, which functions in a somewhat similar manner. There is a numerical score somewhere in a database, but it's never displayed: users just see "your karma is good", "your karma is terrible", etc. This is an explicitly adopted measure to remove the temptation to "game" the karma system -- as soon as there's a number, people want to improve it by all means. You can occasionally see people on the discussion threads here whose focus has shifted from actually learning the language to completing the tree, getting the most coins, having the most followers, getting the most upvotes, etc. -- by whatever means necessary. So a numerical Kudos system would, I fear, result in collusion, sockpuppet accounts, "PLZ GIVE ME KUDOS!!!!11" posts, and who knows what else.
One common feature in this kind of reputation system seems to be that it always requires a lot of time, tweaking, effort, and modification to get it right. Not to say it's a bad idea, but, as with many good ideas, it's more work than it might at first seem.
You have some good points, but I think that any such system is flawed and would take away focus from the learning aspect to the social aspect. Now, while I don't think every site needs a community, I see how one can be useful to Duolingo, you are more likely to get massive upvotes/social points for saying Duolingo is awesome, than for helping someone learn.