Quantifying Online Promotion Efforts?

udhay asks: "Hi -- I'm with a startup that has what we think is a hot new product (it's a downloadable desktop app). We got some venture funding in, and are looking to outsource some of the stuff that we need to do, such as online promotion. "Online Promotion Agencies" are a dime a dozen however, and we were wondering how one would go about rating them, and how one would quantify the results they produce. I figured /. is a good place to ask - any ideas?"