I've only driven a couple and one of those was a diesel one and I thought it was proper shit. The other one wasn't too bad, just not my cup of tea.

The MHD (Micro Hybrid Drive) ones tend to eat alternator belts (the alternator doubles as the starter motor and uses the alternator belt to turn the engine over) which I've recovered a fair few for which I've been told by quite a few Smart technicians is a horrid job to do on them.