Genuine VC posted here on Vertical Marketplaces. Of course Nimble is one of these marketplaces so you can read my posting this here as a form of self reinforcement, but what do you expect. I'm on the bandwagon.
The real opportunity here is in the business model itself – not just providing paid advertising listings (or even contextual relevant advertising adjacent to the listings themselves), but rather actually participating in the transaction as a percentage fee. The more intimate the relationship these marketplaces play in the transaction, the greater the value they can capture from it. As Rentacoder has demonstrated, this level of is engagement is possible by assuming the risk of the transaction, which gives both transacting parties the comfort in "paying" for the introductory services in a substantial manner.