Seems that the Yahoo index is including Google AdWords and other PPC tracking links for some Google advertisers which are messing up their backend tracking and analysis.
Doubtful Google is charging for these clickthru’s, but when you see hundreds of users landing on a Google AdWords specific landing page from Yahoo Search, there’s going to be some weird numbers.
Barry Schwartz picked up a thread in Webmaster World:
Is anyone else noticing that Yahoo is picking up Google Adwords links? I only know because i append all of my Google and other PPC links with a src=#*$!X and my tracking software also appends similar information.
Other webmasters have responded with confirmation of the same problems.
Yahoo Search, Google AdWords