While Yahoo signals a "little bit of weakness in the last few weeks" in financial services advertising, it is directing Yahoo Finance traffic to Web pages monetized by Google ads. Yes, there are less than six degrees of separation on the Web between arch competitive rivals Google and Yahoo.
The Yahoo Finance vertical presents featured Reuters news stories which run "Ads by Google" not "Sponsored Links by Yahoo and Overture Services."
Google is a fan of competitive collaboration; It is not a smart move, however, for Yahoo to be sending Google more AdSense business at the expense of its own ad sales.
UPDATE SEE: Google AdWords: soon over-priced with poor ROI