Besides what others have mentioned, it's worth noting that at this point is almost impossible to hand pick most of your loans. They get dumped onto the market at set times, and most of the "good" looking low grade loans are snapped up almost immediately, so it can be difficult to build a portfolio with exposure to those grades.

What I ultimately ended up doing, and maybe this was their goal, is just to sign-up with their auto-invest system. They lowered the minimum down to something small like $5000, and you can twiddle a few pretty coarse knobs to say what kind of risk exposure you want. At that point it's completely hands-off for me, and I just track the progress - every time I accrue $25 worth of cash from the existing investments, they buy another note on my behalf.

I'd definitely be careful how much cash you throw at this, I thought it'd be an interesting experiment and my portfolio has done fine, but it's hard to quantify the risks. If the economy tanks, how much will the default rate increase? Also as others have mentioned, the secondary market for these notes is really poor - you'd take a huge loss to liquidate your position.