Funny someone should mention Topgear.
Either them, or 5th gear did a test on a Smart, crashed it.
They're opinion was that while the vehicle structure survived, the people inside wouldn't have as the force of the impact couldn't be absorbed by the vehicle (lack of crumple zones as someone pointed out) and as such would be passed to the occupants,
and ultimately that force would likely result in internal injuries and death at speeds other cars might allow you to walk away from.
"while the structure of the car may have survived, the occupants would not have"
That being said, the crash tests that determine ratings are perhaps at lower speeds. We all know of people who have survived horrific crashes
in C Classes. The implication seems to be that at higher speeds and force of impact your chances of survival would be better in a C Class vs. a Smart.
Ah here it is....
YouTube - Fifth Gear Smart Fortwo vs Vauxhall/Opel Corsa Crash Test
and then there's the handling, which IMHO is as important if not more than crash tests, in avoiding an accident in the 1st place. The Stig couldn't keep the fourtwo on the track.
YouTube - Prius-Kenari-Smart
Carl, Please don't tell me you're thinking of buying a smart....