I love P2Pool and having been running it for a while but I have a pretty marginal rig at around 700MH/s and with the latest hike in difficulty I'm just not getting any shares any more.
Sooner or later you should get one. It should all even out in the long run.
Of course, if you start getting shares once a week or something then it's time to switch pool, but it can't be that bad..?
700MH/s at currently 23400 difficulty is ...