Michael Arrington at TechCrunch reported yesterday that Facebook is now twice the size of MySpace worldwide, measured by monthly unique visitors. MySpace is still #1 in the U.S., but extrapolating the traffic data predicts that Facebook will overtake it sometime later this year.  Facebook’s registered users has been growing explosively.

However, MySpace users also used their social network much more intensively.  According to socialmedia blog, MySpace users spent 17.5 billion minutes online compared with 9.3 billion minutes for Facebook, generating 40 billion pageviews compared with Facebook’s 18 billion.

Anyway you look at it, these are staggering numbers.  MySpace claims it is succeeding in monetizing this traffic, while Facebook continues to push for user growth.  For me, the more interesting thing is how these giants will push my world around.  We already know that social media generate the huge buzz we depend on for ‘viral’ marketing with content syndication and links between publishers (see the two above?).  But how is that going to affect the core function of search in the online world?

I don’t think Google is worried.  But search functions can become a lot more specialized.  Think about looking for real time insights into a developing event:  wouldn’t you search Twitter?

Using social networks for advertising has proved to be a real challenge for marketers.  Users want the networks for personal socializing and dislike ads.  Yet, the personal recommendation of a product is the best marketing anyone can get, so marketers aren’t giving up.  Marketing Vox posts that in another attempt to harness the power of social networks, Facebook is introducting Connect.  Connect makes an existing third party website (like Hulu, Discovery or Digg) available to a group of friends to view and comment on together.  In other words, this external content becomes part of the conversation.  Want to watch a video together on Hulu?  Do it through Facebook and share the time with your friends.  This makes the event more valuable to advertisers, in theory.  As always, the ultimate force driving this is how attractive the content itself is:  if Facebook friends share an interest in content that is valuable to them, the ads will be seen.  If the content isn’t any good, forget about it.  So, leveraging the content of a site like Hulu makes good sense — and undoubtedly means Hulu will want part of the action.

Here’s a link to social network traffic reports by Nielsen Wire, courtesy of Jeremiah Owyang.  These are all still growing like the emerging markets they are (fast, in other words), with MySpace still king of the hill.  But MySpace is too big to grow fast (“mature” doesn’t seem right for it, somehow, but that’s the analogy to the stage of economic development for you).  Twitter is the growth leader, followed by tagged.com, Ning, and LinkedIn. Interesting tidbit on the network profiles:  Facebook, LinkedIn, and Reunion.com are most popular among visitors ages 25-34, 35-49, and 55-64, respectively.

Most online marketers I know are obsessing over social networks and social media. How do we market our clients using these autonomous user-driven networks?  Here’s Chris Brogran’s Best Advice about Social Networking with a nice list of links to resources — it’s a start.