I make my living driving large trucks (both tractor-trailers and three-axle straight trucks), and I can tell you that those "Smart" cars are not as safe as some claim them to be.
First of all, they tend to be worse when they're in my blind spot - and it often takes a second look at the mirror to see someone there (which I am good at doing because I have to in order to avoid a collision). The sheer lack of size makes them harder to see than someone in a Corolla, Civic, etc.
Second, the people who drive them seem to think that everyone will "notice" them because of the novelty of the car. Well, folks on a motorcycle might feel the same way. I almost think they deliberately try to stay in my blind spots! They'll match my speed if I try to get away from them.
:bash:
Finally, in the event of a crash, it is nice to have crumple zones and all that stuff - but you just can't substitute mass and metal; particularly if the other vehicle in the collision is much larger. The part about avoiding the crash altogether seems important if you drive a Smart ForTwo, or some other econobox.
Whatever you drive, though, be safe and give a big rig plenty of room. Stay far enough behind me to see my side mirrors or pass on by me quickly - but don't ride along side me if you can avoid it and ALWAYS, ALWAYS, ALWAYS signal your intention when turning or changing lanes.
~ End of rant; off of my soapbox. ~