Unfortunately, this isn't true at all. While Mercedes advertises the Smart Car's 5-star crash rating, what they fail to mention is that this just means the passenger cabin stays intact in a frontal impact. In a car where there is no space for a crumple zone, however, a rigid body is a bad thing. When the Smart Car hits something, rather than absorb the energy like a normal car it's extremely rigid frame instead transfers the impact to the driver's body and most seriously, to his brain as it impacts the front of his skull while his body is held in place.
Top Gear crash tested a Smart Car and determined that while the car stayed remarkably intact, this just meant that the driver took the brunt of the crash forces and would have died. There's no magic here: A car so small that your feet are essentially right behind the front bumper has no ability to protect driver and passenger from the tremendous G-forces involved in a collision. For your sake, I would seriously rethink the whole Smart Car thing.
Here’s a better option for gas mileage when they come out next year. http://www.eliomotors.com
They have a bigger foot print with crumple zones around the driver and passenger. (But people will still probably tip them over.)