Jay Yarrow at Business Insider just penned this piece about Elon Musk's "hyperloop" concept.
While I'm sure that Mr. Must has something very interesting up his sleeve, I just wanted to point out that the idea discussed in that article, an underground vacuum maglev system detailed in a 1972 RAND paper, is utter, fantastical nonsense. Not only are tunnels fantastically expensive and time consuming to build (Second Avenue Subway? LIRR / GCT connection? Anyone?) the idea of sustaining a vacuum in anything remotely that large is pure, unabashed science fiction. It is literally impossible. No amount of money or clever engineering could make that happen. It would literally be the most expensive engineering project in history by a few orders of magnitude, and it would still fail.
My guess is that Mr. Musk - a fully qualified engineer - has nothing of the sort in mind, simply because it is a child's fantasy. However, what Mr. Musk has described, a magnetically propelled super-sonic levitating train, is not much different than magnetic trains that are already all over the planet. The trick is to ensure stability past the sound barrier on the ground, a non-trivial problem, as well as ensuring that friction is low enough. My bet is about 100:1 that this is what is on the table, and not a gigantic vacuum tube system.