The cars have been around in europe for over ten years, and only in the US for about a year so it is a little early to say abot the longvity. However, the motors (mitsubishi) are used in forklifts and other cars (like the Geo Metro) and work really well. Almost all of my vehicles last at least 200,000 miles, I currently have only 8,700 miles on my Smart, but it is only 4 months old. No problems and not that many problems reported on here. Just one or 2 real serious ones but they seem to happen right away.
I you are concerned about the 2yr\24,000 mile you can purchase an extended warranty.
Most common problems have been the battey, and shifter geting stuck but they seem to have that taken care of.
I'd suggest taking one for a drive, or if available, rent one for a few days and see if it fits your lifestyle. It's not a SUV or a Cadallac. It is a lot of fun to drive and if you don't need all the space of a full size vehicle, it works just fine.