Dan Frommer gets to the core of why Facebook’s advertising model is so dangerous to Google:

And then you’ll get to the magic: Facebook’s targeting page. Here, you can narrow your ad’s target by an incredible basket of options. Location, age, gender, precise interests (as volunteered!), Facebook connections, sexual orientation, relationship status, languages, education and specific workplaces.

And Google’s targeting:

Google’s search advertising product, on the other hand, only offers a fraction of this targeting. You can target by location, languages and devices. But it mostly comes down to keywords: What are people searching for or looking at?