All I've ever heard are horror stories about how advertising on Facebook does not work. I definitely don't see how ads on a social network can compete with ads on the largest search engine and almost every ad funded website in the world.
Facebook advertising has been very effective and profitable for at least some clients. I think Google+ shows that Google is terrified of Facebook. I have no knowledge of how Google's advertising revenue is doing, and wouldn't be at all surprised if they still dwarfed Facebook.
On the other hand, google knows it is likely just a matter of time before Facebook gets it right, and when they do they are one of the few companies who could complete at scale with google.
But people spend way more time on Facebook. It's entertainment, whereas Google is a tool. So brand advertising works better on Facebook. It's more like TV advertising.
[0]: http://www.emarketer.com/Article/Driven-by-Facebook-Google-M...
Weird, I know. Actually, I do have an account but only used it to write a Facebook app for a client, not for actual use on that mini-Internet (kind of like Geocities isn't it?)