I have not driven one, but I use Consumer Reports to research most of my car purchases. The car didn't score very well overall. Excellent owner costs and fuel economy (they reported 39mpg in mixed driving) but poor handling and a below average ride. Accident avoidance was mediocre.
In terms of repairs, the '08 has done better than the '09, but still had a lot of minor transmission problems.
Overall it seems they liked the fuel efficiency and manuverability/parking but found everything else to be lacking.
They liked the Kia Rio and Chevy Sonic much, much better. Both got around 30mpg in their testing. The VW Golf TDI (diesel) was their highest 'fuel efficient small car' with 38mpg overall in testing and 49mpg on the highway.
some of their comments:
The Smart ForTwo's tiny size and turning circle make it a breeze to park. Its tiny engine returns excellent fuel economy. But the ForTwo requires premium fuel and there's little cargo room. Acceleration is slow, the transmission is jerky, and the ride is harsh. The ForTwo finished at the bottom of our subcompact car Ratings with a score of only 28 (out of 100)....
...has a harsh, choppy ride and crashes over bumps. On the highway, the ride remains stiff. Exhaust, wind, and road noise add up to a lot of noise, but the engine is often the worst offender. The Smart leans in corners and steering is sluggish, even with the optional power assist. On the highway, it is buffeted by winds or truck turbulence.
...There is a lot of space for two, but you sit close to the doors in this narrow car, limiting elbow room. The seating is high and most drivers found sufficient head room.
...Total capacity for occupants and cargo is 505 pounds.
...Many controls are poorly designed or located. Window controls are mounted too far back on the doors, the door lock button is on the dash, and the hard-to-read climate controls are mounted atop the dashboard, making them a reach.