Mark_A - 8:26 am on Jan 6, 2011 (gmt 0)
Call to action, is phone call or email and tracking on these is asking when we remember, "how did you hear of us?" which usually elicits the not very useful response "on the web" which could mean pretty much anything.
If I were to try to establish the cost effectiveness of the adword, then I believe I also should try to establish the cost effectiveness of the SERPs as it has also a cost. A lot of work has gone into getting our #5 ranking and that has a cost.