I'm willing to bet just abotu everyone in here has. They've been on the road in Europe since 1998, and in the news in America for years. They've even been importing them into the states for a good while now. At least a year. I believe it is Penske-the racing guy-guy is distributing most of them, but not sure of that. They're made by Mercedes, originaly designed by swatch-- the watch people-- and the name means Swatch Mercedes ART.
I'm sure you could find more at Wikipedia.
The mileage on them isn't all that great though. They can be beat in mileage by any hybrid, VW TDIs, toyota echos, and a few other frugal cars that have much better utility, more passenger capacity, and more crumple zone. They are very good at avoiding passenger compartment collapse. But since nothing is there to absorb energy, the sudden deceleration would dislodge your internal organs and generaly do bad stuff to you in a decent crash.
They are kind of cute in a so-ugly-it's-cute kind of way. Maybe that, and their compactness and ability to fit into little tiny spots is what has helped them. They are developing a kind of cult following.