Facebook (FB) has been one of the most aggressive technology giants in the last couple of years in terms of acquisitions. It has acquired scores of companies, including Instagram for $1 billion, and smaller talent acquisitions like Glancee, Tagtile, Gazehawk, Karma and Lightbox.

Since the time it went public, it has seen relatively higher attrition, and the talent crunch in Silicon Valley has forced it to ramp up its acquisitions in order to continue adding talent to its team, besides focusing on its regular hiring tactics.

This week, it acquired Spool, a mobile bookmarking service that was in beta and was expected to launch soon. It will now be closing down its standalone service, and the Spool team will work on Facebook's mobile offerings, focusing on delivering content on mobile devices through Facebook's network.

"The Spool team has deep expertise in mobile software development and a passion for making content easy to consume. We're excited for the team to join and accelerate their vision at Facebook," said a statement from Facebook.

Facebook has been increasingly focused on the mobile space, which continues to worry investors since the company has not been able to monetize its mobile audience as well as it had expected. Since most of its active user base comes from mobile, it is working on ways to not only improve engagement on its mobile apps, but also monetize them effectively. It has made quite a few mobile-related acquisitions in the last couple of quarters, and we expect it to continue doing so, going forward.

We currently have a $33 Trefis price estimate for Facebook, most of which is derived from its social text and display advertising business. It competes primarily with Google (GOOG), Microsoft (MSFT) and Yahoo (YHOO) in the online advertising space.

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