What are you thoughts about various incentive mechanisms to promote users active. There was a interesting talk in #startups last night about this, and I think a bigger audience would find it interesting as well.<p>For example the most basic method is Karma/Points for submission and getting voted up (such as HN, Reddit).<p>A variation of the above system is propagating points from child-to-parent. For example voting a child item/comment will also give points to it's parent (or fraction of a point) to the parent. This way items that start active discussions or activity with child submissions are promoted with more points.<p>Another is a badge/achievement system. StackOverflow is one, where users can collect various type of badges for doing certain things or reaching milestones. (Someone brough up Xbox live as well, where achievements not only for positive aspects, but also for glorious fails... so who knows). A twist on this is not only having badges, but also having badges convert to point values.<p>Collecting or having points them selves imho is not all that useful other than for bragging and/or pulling rank. I think being able to redeem/trade them in for various features or more leverage on a activity in the site is much more useful. For example in SO's case, you can trade in your points for bounties on questions.<p>Did I miss any other major point/incentive type systems? So, what are you thoughts/comments/criticisms regarding this?