I was a bit dubious at first. I didn't think it had much to offer over PBeM or PBP.
I'm playing in a run through of Revenge of the Giants with a fellow who I'm not sure if he's got an EN World account or not. He's done two things that sell the concept for me.
1. Taking advantage of the "wiki" nature of wave, where anyone can insert things anywhere. Basically, he starts a scene with a long description and narrative (maybe a dozen or so short paragraphs). Then, anyone can just jump in at any point in the narrative and add in their characters actions. In this way, say, I might respond to something near the end but someone else can seamlessly take a cue from something near the beginning, and the structure of the narrative remains chronologically-obvious.
2. Something he's come up with called 'Skill Tags'. As an example, I wanted to examine a giant and wrote...
Primus leaps astride the nearest giant and shifts back into his humanoid form. The warforged picks through the giant's clothes with care, looking for any sign of anything strange or out of the ordinary. [Perception:26]
Then he came in and edited that to:
[sblock=Maybe minor spoilers for Revenge of the Giants, not sure, better safe than sorry]
Primus leaps astride the nearest giant and shifts back into his humanoid form. The warforged picks through the giant's clothes with care, looking for any sign of anything strange or out of the ordinary. He sees some unusual markings along the neck of the leader, a strange glyph branded into the flesh. Primus also makes note of the scraps of metal plate adorning his shoulder and intended to be armor of some kind. It is the same brand of metal that the blade is made of.[/sblock]
So on a readthrough, it continues as one unbroken narrative rather than a bunch of posts which need to be pieced together.