The three things that Freakonomic's authors will tell you that influence someone's decisions are: economic, social and moral. In terms of influence in commerce:
Amazon, Ebay and Google own economic.
Facebook owns social. Obviously Twitter is coming, but not integrating with brands front and center the way Facebook does.
No one owns moral. Maybe a non-profit brand like the Red Cross. But most tie-in moral into their offering. No one does it exclusively for commerce. Tom's Shoes aren't bought just because they're a moral company. Much goes into the messaging on the economic and social side.
The best brands tie in all three.
But, what happens now when Google combines economic and social? Intent and demographics and context?
The difference between Facebook ads and Google ads are intent. Most people don't search Facebook for their nearest restaurant or a shoe they want to buy. Sure, they spend more time on Facebook but when it comes time to INTEND to buy they go to Google.
The new place to play is ads (insert daily deals here too) in context and discovery: where you live, where you socialize, where you are right now. Best of all, the ads are smart and come to you...but they don't care about your real intent...they want to form your blank slate of a day with their intent. Native apps (iOS, Android, Windows) and HTML5 apps with geolocation and social API integration are just the beginning.
With a new layer of social search results you be able to get your economic + social influencers in one place.
For those that don't care what the experts say, they just want to know if their friends own it, bought it, liked it, etc...you're all set.
Wait, I guess if you're friends would just join Google+ or Google will integrate Twitter and Facebook a bit more, then you'll be all set. :(