Not sure if this will be helpful, but I have had good results in a couple different pbps I was in by arranging to meet via skype or similar and using live text chat. This allows people to avoid having to narrate their responses and use their composition skills, while still allowing their to be a certain synchrony of intent that insures that things keep moving. Also, the chats can then be copypasta'd into the pbp thread, which allows a nice record of what was said and done.
This worked really well for in-depth role play and characterization, which are big facets of Exalted, so I thought I'd mention it.
Unfortunately, there were all very small groups (2-3 ppl max), cause otherwise syncing up meeting times is virtually impossible.