Google is buying "Plannr," a "social calendar" for mobile devices. The app itself is largely unremarkable and the acquisition may be about buying the small team (of two) behind Plannr. One can imagine a mobile-social event planning or calendaring tool being one of the many nodes of Google's evolving and emerging social strategy.
And, CBInsights comparison of the tech companies and their acquisitions in 2010 to date revealed that "Google leads with 23, Facebook has 6, Apple 5, Yahoo 3 and Microsoft 0."
Google made five acquisitions in 2009, three in 2008 and 15 in 2007, the year of its greatest M&A activity until this year.