Live Journal considered limits on the number of posts a user can make per day. They are hosting close to a million user ids on the system, and that population is large enough to include a few script kiddies trying to break their servers.
However, if you’re trying to stop script kiddies, then you don’t need something as draconian as hard posting limits. And since they aren’t considering limits on comments, then that leaves a hole for someone to exploit. And a determined person could still launch a denial of service attack since Live Journal still has to check the user id against the post limit, which has to be at least one database query.
I think that attack is something you defend against at the network level.
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