It is said that in the near future Yahoo will drop the Overture brand name, and rebrand it as a Yahoo service. This would be needed because Overture is not even half as well known as Yahoo
The concept is really quite simple, Google AdWords is Google. Yahoo Mail is Yahoo. GMail is Google. There is no reason to keep Overture branded as a separate entity. Yahoo did the same rebranding after its acquisition of Inktomi and the transformation of the old Inktomi technology into Yahoo Search. Google has done similar rebranding with their acquistions, skillfully transforming Picassa into Google Picassa.