I almost went with Siri's continued ineptness 14 months after launch, but when asked by Heidi Cohen about the biggest marketing surprise of 2012, I pointed to a public offering gone bad:
"The biggest surprise was the freefall of Facebook stock following the IPO. Sure, the company went public without a complete monetization strategy, but the company was such a darling that a softer landing was more predictable. But, like Apple, by the end of the year, shareholders demanded extraordinary business results for extraordinary stock prices. And that’s a good thing."
Unanticipated events named by other marketers are here http://heidicohen.com/2012-biggest-marketing-surprises/