The update by Google to make social signals more prevalent in search results is fairly significant, though the absence of Facebook is of course notable. While these results have been seen in searches for a while this update brings them higher up in the results, mixing them among the other listings as opposed to lumping them all together at the bottom. Most importantly (at least to me) Google also now notes when a link has been shared by someone on Twitter, adding relevance to those links.
What I like about the way this has been implemented is, as John Battelle says, it shows that Google has broader goals for how it brings in social signals and doesn’t just want to count on Facebook as the end-all-be-all. If social search is going to work it needs to not be tied to one, two or even a dozen different social graphs, it needs to account for hundreds and use them all as just one signal each. Only that’s going to allow it to evolve in a manner that’s useful for searchers as networks continue to grow, change or fail.