Under the agreement, Google AdWords ads will be shown in Yahoo Search results when their cost per click value is expected to be higher than Yahoo Search Marketing ads, after a revenue split between Yahoo and Google. The deal expands Google’s ad distribution tremendously and also gives Yahoo the jolt it may need to keep on going. Ironically, it was Yahoo which gave Google search technology its start in the limelight when it licensed Google to power Yahoo Search about eight years ago.
Not really a merger per se, but you will see yahoo displaying google ads in certain circumstances. However, this is probably a first step in things to come.