I have a friend who is in his late forties, and for reasons we won't go into here, never really developed his career. He learned basic programming skills in .NET a few years ago, and got a job with that, but now he's found himself unemployed again, with nothing to differentiate him from the rest of the pack.
He's a very bright guy, and capable of learning new technologies. I recommended to him that in his unemployed time he should try and learn a niche or emerging technology, so that he can have some feature on his resume to distinguish him. But I don't really know what's out there, our how in demand any given technology is.
What would you recommend he learn?