I dipped my toe in the water for a couple of hundred.
You lend in units of 10 or 20 pounds, so the risk is spread.
You can elect at what rate you lend, within reason.
Had one bad loan, but am getting good returns.
Fair investment as part of a spread.
I've been a zopa investor since it's inception, I am no friend of the banks. For me the returns have been very very good, losses through default were minimal and more than cushioned by the interest rates I chose. My investment is well ahead of banks and building societies and with recent stagnation few shares, or trusts would compete.
The way money is lent has however recently changed, the new system of safeguarded offers is supposed to be more secure, but I liked the old system where you chose your rates and made your own offers. I'll wait and see how it runs. There are other versions out there, "Auxmoney" in Germany for example.