Early investors who have chosen not to pony up more have gotten their investment diluted into a tiny sliver. The round was at the same price as the D round, but since it's less than a tenth of the C round and less than half the A round it reflects a belief that Prosper is a much riskier investment than it appeared to be in 2007.
On the other hand, it means Prosper will be around for a while and has a chance of increasing its base to the point of viability. Its short term viability, a serious issue in the last few months, has been settled for the time being. This gives it some breathing space.