Website owners that use AdWords like to use a variety of third party tracking tools to measure the performance of the campaigns. Comparing numbers reported by various systems will help give a bigger picture, and sometimes detect possible click fraud. One of the easiest (and usually least expensive) ways to tracks referrals is through a standard web analytics system often provided for a minimal charge with most hosting packages. The referring URL's can then be examined and this is a neat way to also find out about new "free" links coming to your site.
A curious thread was started recently at WebMasterWorld Forums that claims a referral attributed to a Google paid click came through Yahoo!:
I got a click from a referring URL that contained: "us.f314.mail.yahoo.com/ym/ShowLetter?MsgId=" I am assuming this came from an email that was opened by someone with a Yahoo account. How do you distribute AdWords thru email? Is that considered part of the content network? How does it and under what circumstances does it happen?
The discussion that follows starts of fairly normally, with people asking for more information. Then the "official" Google AdWords rep joins and asks for more information. He (she?) followed up yesterday saying that G's "interest had been peaked." The following posts are pretty funny, with a couple of members suggesting that G should bid for the information.
Join the thread and help solve the mystery at WebMasterWorld Forums.