Web Analytics Blog | Occam's Razor by Avinash Kaushik - http://www.kaushik.net/avinash...
"My recommendation is simple: 1) Understand each stage of the customer purchase life cycle. 2) Map your keyword portfolio to each of those life cycle stages (curious, awareness, interested, consideration, purchase etc). 3) Measure success of keywords in each step differently. No: “everyone’s got to convert!” Early stage / upper funnel / long tail keywords are significantly cheaper, let’s hold them to a lower standard." - Jeroen De Miranda