I bet MeFi could be fixed in a few months if they hired a real SEO expert, ie someone who understands the underlying ranking algos and not just the usual voodoo bullcrap. The site is probably just tripping a few red flags, it could be something as stupid as an accidental link loop in their dynamic content.
I'll give it to Google, once you find your sin and fix it, your traffic will come back, maybe not 100% but a significant recovery. (Unless you have done something really dumb/blackhat like paid links.)