In the RP i've been most active in (Precipice of War), we generally have policed writing styles. Third person past tense has more or less been the rule, and we've stressed the necessity for fully fleshed out posts. The caveat is that it moves slowly, since many of us write upward to 5k words in each post, probably averaging about 2k if I were to guess. The reward is that RP more or less holds together. 

Another thing we've done is, when we want to have characters belonging to different RPers interact, we write out collaborative posts in PM's so that we produce a complete post rather than a bunch of conversation blurbs. It comes out looking sort of like [url=http://www.roleplayerguild.com/posts/2817464]this[/url]