Efficiency was close to zero with an Avalon mining stratum on p2pool.
Odd and worrying: you are not the only one having tried mining on p2pool with Avalons. I don't follow it closely (forums are not really the best for bug reports, I have to work from memory and I'm on painkillers right now...) but I know people have managed to bring Avalons at least in the 50-75% efficiency range right from the beginning and made progress from this point (maybe not with stratum).
I suspect there's at least one Avalon user on P2Pool for quite some time now which uses it without apparent problems given his payouts (185Kip6odGYs4eSHD6DYsWVDJBg2DNLfiV since 2013-09-04 with an effective ~65GH/s hashrate).
It was a bug in Avalon's fork of cgminer, which Avalon refused to fix.
forrest, the guy who wrote p2pool, ended up fixing it on his end which isn't an appropriate way of fixing it. Avalon users mine on p2pool fine now.