Badges is one of the big items that needs to be built and going on top of the development priority list.
Another suggested dynamic we can explore:
The top 5 experts for the week get a Pro tag next to their name across the entire site. This privilege would get recalculated each week. i.e. If you have Pro tag this week, you'll need to be in the top 5 experts again next week to retain it.
Here's a great little 12-pager on gamification:
http://www.bunchball.com/sites/default/files/downloads/gamification101.pdf
Update Feb 11:
Here are some stats of users with karma > 100:
Karma.......Num Users
> 1000..........127
500-1K.........132
100-500........9,712
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Update Feb 13:
We've almost reached a gamification outline that I'll post here soon to get everyone's approval. Apart from just badges like SE, I think we can innovate in this component to really make the community sticky and add value for contributors.
Update Feb 22:
Pro badge is live. We're working on a much larger gamification plan that will take a little more time to build out. It'll be well worth it :)