I just watched this youtube video from the Chief Economist, Hal Varian, who explains some fundamental profitability terms in a surprisingly "non-economist" fashion. By this I mean it's relatively easy to understand. If you can get past all the acronym-induced confusion and fear of percentages, you'll find this video particularly helpful when it comes to thinking about how much of a return you're getting from AdWords. Perhaps more importantly, it'll help you think through bidding strategy with a sense of direction.
In the first part, he discusses how to find your Value Per Click, and how that can guide you towards a profitable bidding price.
In the second part, he explains how to find Incremental Cost Per Click, and how this can deliver an optimal bidding strategy for gaining the most profit.
http://www.youtube.com/watch?v=jRx7AMb6rZ0






