And the reason they want social Open is to commoditize it. (Same strategy as Android.) Everything a commodity except for search is the perfect world for Google.
Facebook has excellent information on users interests. As opposed to MySpace and Twitter, most of the data on Facebook is not crawlable. It's private data, which means that Google is completely locked out. Even if it was crawlable, the data is not as valuable since Google would have to try to interpret it, while Facebook knows what it really means.
Summary: Facebook is an existential threat to Google's two major lines of business AdSense and AdWords. This is going to be a huge drawn out battle. Sit back and enjoy the show.
If they integrate all Google products with Google+ tightly, it will cover entire web for most of the internet power users aka Geeks.