Strongly disagree with Pachamac's vision of collaborative posting. If you're pming back and forth, you are definitely doing it wrong. There are several mediums of collaborative writing out there that make it far less of a harrowing chore. It's not even about a constant back and forth that is basically several posts in one (I have done collab posts upwards of 3000 words), but it's about the dynamic interaction that the kind of collaborative posting allows. Admittedly, yes the posts are huge. However, if they're spaced and paced properly from scene to scene they are far more pleasant to read than the big mess of... five paragraphs about a characters perspective on the scene.

It definitely helps when everyone is from the same continent, if not time zone, but when you're less worried about interacting with EVERYONE ELSE in the RP and just more specifically with the characters in your vicinity or relevant plot arc, this ends up going at a very comfortable pace where characters can actually accomplish something in a feasible amount of time. 

Whereas typical play by post in advanced without any collaboration really does feel like back and forth novella without relevant interaction more than half the time.