I can think of three possible reasons (I claim no expertise here) to doubt that FISA orders and phone metadata are completely useless against terrorists even if

I can think of three possible reasons (I claim no expertise here) to doubt that FISA orders and phone metadata are completely useless against terrorists even if (as seems likely) serious terrorists know to steer clear of Skype, Facebook and friends. 1) By monitoring Internet services like these, the NSA denies their use to the terrorists. It's not as if exclusively using couriers, dead drops and the like has no costs to an organisation (say, have you moved off GMail yet?) Apparently some fairly serious terrorists are using the Internet in more secure ways, but the spooks have some ability to go after those too. 2) Any big network or organisations is going to have slipups, no matter how good it is. It would be hard to imagine that no serious terrorist ever gets lazy, or decides to take a risk under time pressure. 3) There have to be a lot of guys who start out as Facebook jihadis, and only later get serious and realise (or have it explained to them) that they need to stop making it easy for the authorities to track them. But by that time they'll already have left a useful trail of contacts and activity through FB. (By the way, that's one reason why I think it's wrong to assume that PRISM has been useless even if it hasn't stopped any specific attacks. Realistically, that kind of intelligence is going to be less about discovering big plots just in time and more about gathering enough information to locate and move on terrorists - espcially if you can then turn them into informers. Running "touts" is central to effective counterterrorism, if history is any guide.)