My final experience in BTCJam after almost a year, I've invested in 9 loans of A or A+ borrowers.

5 repaid.
4 defaulted.

Almost all of them have a D- or E rating by now.
This means a 44% of probability of your money to be gone once you invest it.

I started with 1 BTC for trying one year ago, now I have 0.1
I will not be posting any opinion or conclussion, this is just my data. Just for all you out there to make your choices.