"Search, Plus your World"
This is probably stating the complete obvious, I know.
Just a theory.. "Search, Plus your World" isn't about improving search, it's about getting people to start using Google+ more.
In LinkedIn's early days, I remember a lot of people having profiles but nobody really using it that much. Then over time, Linkedin's Google juice went up and all of a sudden, whenever anyone googled themselves they saw their Linkedin profile.. so of course, out of vanity realizing other people would see their profile now, everyone thought "oh shit i better fill this page out more"
So Google placing Google+ profiles high in default search results is maybe less about helping searchers find the best search result, and more about giving distribution to people's Google+ profiles so people are motivated to finally start using it more.
If so, it's a smart move.
update: I just noticed that Google puts a "Update your profile, it's only x% complete" link on the search results page when you google yourself.. To me, this pretty much confirms it. Google is smart.