If you want some idea of what the risk level is like, here's a little matlab sim I made - it simulates the first 250 blocks profit/loss for a PPS pool at some given fee. To give some visualisation of the risk distribution it runs this 100 times and you can just plot that:
5% fee:
10% fee:
15% fee:
15% being really pretty meaningless though - if I struggle to find enough people to mine at what amounts to a negative fee then good luck finding substantial hashrate that wants 15%... Unless you start paying cash-in-the-mail or something useful to a wider audience (50BTC have had great success with this although their fee is 3%) then I doubt you'll get any real hashrate that way.
