I'm not sure why people would mine on a p2pool based pool when they could just run p2pool themselves but at least it wouldn't matter too much if people dropped out since the p2pool network as a whole would enable blocks to be found faster vs a lone pool.
I run p2pool but when my Neptune arrived I found I could only get under one terrahash on my p2pool pool but 3.4 terrahashes on mmpool.
For some reason p2pool just wasn't handling the high hash rate.
I wanted to use p2pool though, and still do use it with smaller hash rate, so as to include coiledcoin and geistgeld in my merge.
Leaving them out didn't help my p2pool handle the high hash rate though.
-MarkM-