It has just dawned on me that one of the places I have deposited part of my modest savings, the lending site Zopa, doesn't have a government-backed guarantee - unlike high street banks and credit unions. Yet the curious thing is that, despite all that and the global credit crunch, Zopa is enjoying a boom. In the third quarter new borrowers soared by nearly 50% to 3,700 compared with the previous quarter. Why is this happening - and is it safe?