+1 and the persistent Like
With +1 Google seems to have gone about social differently. +1 is a highly scaled down version of a social network - the opposite of Facebook. Facebook built the interaction feature-set first, then used the Like button to spread it. Google's approach seems to be focused on building out the +1 button and eventually coalesce the rest of its sharing services around it.
+1 has two things going for it - it is persistent and contextual. Persistent because unlike the Like button, the core idea for +1 is not to broadcast the action to everyone. When you "like" something, that act itself is shared by Facebook. Which works for Facebook, because communication is what Facebook is all about. But +1 is more persistent; it hides in the sandwich layer between web-content and you - the search engine.
Persistence is important, because this shifts the playing field away from conversations - which Facebook and Twitter are good at, to algorithmically mining history - something Google is great at. This is where context comes in. Google owns your landing page on the web: the search results. It is a powerful page, and is also contextual. Unlike the static Facebook, Google's use of +1 can morph itself to add context to what you are in the mood for at that time. Unlike a cacophony of likes, you instead get the few +1's that are highly relevant to what you are doing at that time.
This is the strategy that worked for Google in ads, and the bet is that it will work for social as well.
The problem for Google's social has not been building out social feature sets. The biggest impediment has been changing the nature of social to fit with Google's strengths. +1 could well be the game changing strategy that Google so desperately needs.