Google has silently released a personal profile service, whose purpose is to "give you greater control over what people find when they search for your name". Everybody has searched for their name once to see how well (or badly) they were "findable", and Google promises to give your name a higher ranking if you fill your profile page.
Now this narcissistic feature based on Google's big gun, their search engine that everybody uses, is actually a smart stealth move towards a social network that doesn't say its name. Your profile can contain information that you only want to disclose to your GMail contacts which are now named "friends". No need to recreate a social graph, it already exists in your mail account. And if you have an Android phone, Google knows your close relatives since your phone's address book is sync'ed with your GMail contacts. You can even grant special permissions to the phone contacts marked as "favorite".
This profile page is not – yet – a threat to Facebook, since it only shows things about you, and not about your friends. But how long before Google adds OpenSocial gadgets to the profile page and merges it with iGoogle? And how long before Google aggregates news from the various URLs about you it invites you to publish (blog, photos, twitter, etc) and kills FriendFeed?
So this profile page looks like the first step towards a "natural" social network, i.e. a network you don't spend time to build, because it's based on your daily communications with people by mail, IM and phone. Now I personally don't use GMail, but having and Android phone requires me to have a Google account and populates my contact list. Creating a Google profile page connects my identity and my other sites on the web (Flickr, Twitter, my blog) to my Google account, thus creating my "Google identity" that their search engine will promote.
Google's social network, Orkut, never really took off. But over time, they have created many of the pieces needed to build a serious social network that doesn't say its name because it doesn't have to, because you don't call your real life friend and family a "network".
Is this a deliberate strategy from Google, or just one more feature that has been developed more or less independently by one of their engineering groups? It's difficult to say if they really have a big picture in mind, because of their decentralized organization. But someday one group will decide that it's fun to connect the dots, and Google will become a real threat to Facebook. I'm not sure though that we will win by switching from one giant to an even bigger one.