Smart cars have been around for a while in the UK now... a good few years. Yes they are compact, yes they are economical, yes they look kinda cute... BUT they are not so great in an accident, it doesn't look like there is much space left for your legs after the crumple zones have collapsed. If you do a Google search on images of Smartcar crashes you'll see what I mean. I don't fancy the idea of being in a head on crash at say 50mph in any car let alone one that's just a little over 8ft.
I have a few friends that either own one or have owned one in the past and all have said that they don't feel 100% safe in them and that they feel unstable to drive. One of my friends rolled one, completely over turned it on a corner in some wet weather and it wasn't like we'd have torrential rain either!
This is obviously just my input though...