The Smart car has a rear engine which minimizes any substantial crumple zone in a front-end collision. In effect, the driver and passengers are the crumple zone and if hit hard, you will not likely survive.
Gas mileage may be great, but you compromise a lot. BTW the back won't hold much more than two grocery bags - hardly enough for the family. It is supposed to be good on snow, but how about IN snow, like 4-8 inches of it? It also appears unstable if you corner it too fast.
There are plenty of better small cars out there and at much better prices. Check out Chevrolet Aveo, Pontiac Pursuit, Saturn Ion Ford Focus etc.