Zynga is one of the largest risks to Facebook, accounting for 12% of revenue. If the relationship were to deteriorate, that is a significant portion of revenue Facebook would have to make up elsewhere, or risk seeing revenue growth slow, or even contract. Zynga's relationship expires with Facebook in May 2015.
Facebook has mentioned mobile as an impediment to growth, having listed it twice in the risk section of its S-1 regulatory document. Despite that, the mobile advertising market is expected to reach $2.9 billion by 2014, up from $1.6 billion in 2012, according to BIA/Kelsey. Facebook has addressed this issue, most notably buying Instagram for $1 billion.
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