I have about 7200 miles on mine (Picked it up in January 09) and the only thing was the transmission put it self into limp mode, and after SmartUSA talked to Smart of Germany it was deemed as a fluke and if it happens again than its something wrong with the transmission, this happened at around 2500 or so... and nothing has happened since.
I've so far had no other issues, and love driving the car everyday.