What's really irritating is that it was Yahoo who sued Google before their IPO. Fool me once, shame on you. Fool me twice, shame on me.
I don't think Facebook is going to stand for this. Obviously, I don't have access to Yahoo's patent portfolios, but it just seems frivolous. If they actually had a case it seems they would've sued a long time ago.
And Google did bite. I read they gave up some 2.7 million shares to Yahoo. It worked once for them, so it looks like they're trying it again.