Each site basically works the same way. Investors can open an account and inject it with some cash. They can then loan that money in small chunks to borrowers who then agree to pay lenders back over a certain period of time. And they'll pay interest at rates anywhere from 7% to 30%.

For borrowers, these micro-lending sites are great because they offer an opportunity to receive a loan without going to a major bank or putting up anything of value for collateral like a house or car. Many people use these services to obtain low interest loans which they use to pay off a high interest credit card. Others invest in equipment or goods for their businesses.

For lenders, the sites offer an opportunity to get a higher return than they can get from more secure investments like CDs. Of course, there's an inherent risk here. If you loan someone a few thousand dollars and they don't pay you back, most of these sites don't offer any sort of protection. But you can minimize this risk by diversifying your loans. Rather than give one borrower $1000, you can give $50 to 20 people. And you can decide who to give your money to after reading about their credit history. If you'd rather be less involved, Proper recently launched a Portfolio Plans feature that lets you set criteria for making loans automatically.

Probably the most intimidating thing about Prosper, Lending Club and other peer to peer lending sites is the fact that they're all so new. Prosper is one of the oldest kids on the block, and it has only been around for 2 years. Since every Prosper loan has a 3 year contract, that means even people who have been using the site since the beginning probably haven't received a full return on their investments yet.

If you're looking for something a bit more secure, you might want to check out Zopa. Like the other services, Zopa lets lenders review a list of potential borrowers and decided who to help. So it gives you the same warm and fuzzy feeling that you're helping someone while making a few bucks. But unlike most other micro-lending services, Zopa partners with FDIC insured credit unions. That means your investment will be insured up to $100,000. So if a borrower doesn't repay a loan, you don't lose any money.

The downside of Zopa is that the service doesn't offer the kind of interest rates that you can find from Prosper or Lending Club. Instead, Zopa investors are asked to open a 1-year CD, with a current rate of 4.25%. That's better than most CDs right now, but nowhere near kind of money you can make with riskier endeavors. Still, if you have a low tolerance for risk and are tired of watching your money accumulate 0.25% interest in your savings account, you might want to check out Zopa.

Do you have any experience with social lending sites? Have you invested or borrowed money? What have the results been? What lending services would you recommend? Let us know in the comments.