We have had a smart for over two years. My husband uses it for commuting and it has saved us a lot on gas! We really like it- inside is feels like you are in a full size car, and we are both pretty tall. A lot of our skeptical friends were very surprised after getting inside, they kept saying "oh it feels like a real car!" And even I can parallel park it LOL.
They are not great in serious snow (over six inches or so) A little bit is not a problem. The interstate is not a problem, it maintains highway speeds with no difficulty. And the crash safety ratings are quite high. My only complaint- it has a stiff suspension, if you are driving on badly rutted/pot-holed roads, you will feel it more than usual.