That's a perfectly good application of a reputational economy. There's pretty much infinite possibility. I'm not sure if it has been explored in fiction better than Doctorow's Down and Out Magic Kingdom, about a post-scarcity, post-singularity society with a reputational economy. http://craphound.com/down/ Available free online under a CC license.
gnus email/news-reader already provides, such a fature via scoring. You can score somebody up/down. At a configured threshold, you dont get to see the posts/articles from such folks anymore. love to have something like this in gmail.
High karma could move your mail towards top of the pile for people that don't know you (VIP).
Or posts/mails could be filtered based on karma thresholds.