Excellent two-part article, by David Skok of Matrix Partners, about the economics of using salespeople in a SaaS startup. Part 1 and part 2 are both extremely interesting, and although they're long, they're essential reading for any B2B SaaS startup that is nearing the critical stage of having found product-market fit.
It also makes a good case (if such a case was needed) for why VC funding can be essential to winning a market, once you've found a repeatable, scalable sales model.