The social media acqui-hiring trend is heating up. Last week, Facebook acquired the social conversations start-up Branch, which comes with the social bookmarking service Potluck, to build out what Facebook calls its Conversations Group. The team at Branch was invited by Facebook to do what its always done but with Facebook support and capital behind it to "build Branch at Facebook scale." That kind of invitation would be nearly impossible for any entrepreneur to turn down, and it signals a growing trend.