NO WAY ... FB will not buy it even at the current $8B market cap. FB will more likely buy STVI cheaply for $200 million. It would be in Google's best interest to buyout STVI now since it is ported in Android to make a dent in Facebook, before FB's IPO.
What possible reason would Facebook have to pay money for this company? They can just replicate it on their own and modify their own website in a way that blocks, or severely limits, external players like Zynga. It makes no sense for them to buy.