@Wen I have no direct experience riding them myself; I had heard they're faster than bicycles and that makes sense (at high speeds air resistance is a huge factor), I just meant slower than cars (which are cheating by throwing vast amounts of energy at the problem).
Maybe I'm overestimating the difficulty of sharing the roads with cars, but around here (Romania) a worryingly large percentage of drivers will rage at and actively swerve towards bicycles, and road accident deaths are pretty high.
There are certainly places where velomobiles would work very well right now - the Netherlands being the obvious example, but anywhere with a bit more of a safe driving culture than here.
Last time I drove on the motorway here I had a little day dream about all 6 lanes being used by bicycles and velomobiles. That's what I'd like the future to look like :)