I've built a HN-based site that uses karma as a currency, which I submitted a week ago, to little fanfare :) http://news.ycombinator.com/item?id=2359935

In the scheme I'm trying, it costs you karma to upvote or downvote, which gets converted to non-spendable clout. You get a small portion of karma everyday, which increases as you have more clout (and followers, another aspect I added). If you have spent all your karma, you cannot submit stories until you earn some. Here I was trying to limit the effect of users that are new, and of those that have not contributed appreciated content or comments.

That said, you've got me rethinking the idea of karma for submissions... It might be better to have submissions only increase clout. -Therefore, it will only slightly increase a user's karma-earning rate. Good comments will be the best way to get karma. Yes. I am going to try that. Thanks!