I'm mining on p2pool\p2pool and p2pool\jtoomim (S3 miner set to load balance). The share dificulty of the pools are very different. On p2pool I have 34 shares in 3 days, but on jtoomim I dont have any shares over the last 3 days and my projected BTC is 0. The exspected time to share is only 8.6 hours.
The initial share difficulty on p2pool/jtoomim is by default higher due to a bug I ran into with nodes with very high hashrate. If you have low hashrate (e.g. less than 3TH/s), it can be a good idea to manually set the difficulty by adding something like +512/65536 after your Bitcoin address in the stratum username field.
https://bitcointalk.org/index.php?topic=18313.msg26151135#msg26151135