As soon as the difficulty rose to 268 m without anything changing at my side (after three months working perfectly) I stopped receiving payouts. After a week I ended up with one pay out of a very low amount as previously wrote in a previous post, but p2pool has paid out about 17 times. I had noticed that I couldn't get a successful share before the pool solved a block and when I did manage to get two , one was orphaned.
That's the problem with a 'small' (yes anything under 100Gh/s is now small) hashrate compared to both your chosen pool and the total network rate.
The only way to have kept the amount more-or-less constant would have been to outgrow the %age changes and added 200 times your hashing power this year !