I would be interested in seeing more places try posting limits. It's easy for someone to shoot off hundreds of thoughtless messages, but it takes time and effort to make a single thoughtful post. A minority trying to do the former is going to inundate those doing the latter. And for those (probably most of us) who do a bit of both, it's likely that our less thoughtful and more rapid fire output is going to dwarf our thoughtful output (just because the latter requires so much more time and effort).
Even in the cases where someone provides a lot of thoughtful output, a minority of active users can often drown out the majority of visitors. It would be interesting to see what kinds of communities would develop if there were efforts to encourage more even output.
I like the concept, though I very strongly suspect it would be gamed.
Creating a system for imposing a cost on persistent identity -- not "real name" identity, but some form of valued persistence -- and then imposing rate-limiting, could be useful.
Reddit does put posting limits on new and unverified accounts, by subreddit. To the point of only one post every 5-10 minutes, if I recall (I've tripped that filter a few times).
Or as I've said a few times: "Who are you?" is the most expensive question in information technology. No matter how you get it wrong, you're screwed.
The problem there is that it is certainly possible to legitimately post hundreds of times a day. I mean yes, someone who posts or votes too much could be a troll. Or they could be a perfectly good, yet exceedingly dedicated community member with a bit much too much free time and a lot of passion for a subject. Limits like those tend to screw over more active users in general.
Even in the cases where someone provides a lot of thoughtful output, a minority of active users can often drown out the majority of visitors. It would be interesting to see what kinds of communities would develop if there were efforts to encourage more even output.