In an unexpected move, AOL has acquired social network Bebo for $850 million. A move into social networking is interesting for AOL given that portals have traditionally dropped the ball when it comes to social networks (albeit, mostly homegrown ones).

It’s also an interesting development in the wake of Google’s comments that monetizing social content has proved harder than it expected (referring mostly to the MySpace contextual ad deal). For AOL, it’s unclear how it will integrate Bebo with its Platform-A ad network (Yahoo! currently serves ads on Bebo).

On the upside, between AIM and Bebo, AOL will own a social graph consisting of $80 million people (Facebook has $67 million registered users). Bebo has also been popular in the U.K., Ireland and New Zealand, and plans to push further in the European market this year, which clearly jibes well with AOL’s international aspirations.

We’ve reached out to AOL for more insight and will provide more later.