Yeah Zynga and Facebook are doing badly. So what? LinkedIn is killing it. There are other success stories. Maybe the bubble in these two company's valuations has popped, but they were overvalued to begin with, not a big loss for me.
"for me" is important here. While I fully agree that FB, and (especially) Zynga were both overvalued, the near-constant deterioration of their stock price is very visible - both to Wall St and investors. Perception is king, and it's not just "ours" which matters. What the public sees is the tri-fecta failure of 3 super-hyped tech IPOs (Groupon, Zynga, Facebook).
edited to add : It's also very worth noting that the perception of FB being massively overvalued may very well have been highly confined to "insiders", or those close to tech.
When I speak with my non-tech friends, most of whom are highly educated (law, medicine, etc.), the general reaction to FB's decline is one of surprise. For instance, I often hear that "everyone thought the price would go up!".
In addition, they've proven that the 'business social network' has value, and thus they're starting to see competition where they didn't before.