We have run a Smart car and trailer for about 2 years. It's actually my wife's car and has been specially adapted with infra red controls for her to drive single handedly (she had a stroke). She loves the car for various reasons. It's small and manoeuvrable. The doors open wide and the seat height means she can slide straight in. It's auto and has all the trimmings of bigger and more expensive cars. eg. 2 stage air con, electric sunroof, electric mirrors, cd player, electric boot lid opening, electric windows. It's liberated her life.
I on the other hand drive a new BMW 3 series. However when we go out together I insist we take the Smart so that I can drive it. It's so much fun. I drive in tiptronic mode and love the way it can out drag a lot of cars, it's fun watching there faces!
There are some points worth noting and they have been mentioned before. eg. The hard and choppy ride, no spare wheel etc. All cars and motorhomes are a compromise in the end(the perfect vehicle doesn't exist) the Smart being no exception, but the good far outweighs the bad.
We tow the car on a Brian James, Bantam trailer (see photo section - page 1, under the name 'biggermac') and the balance and stability are exceptional. A recent drive to Southern Spain proved how good it was. 3000 miles mile round trip and we hardly knew it was there. We even took it to Austria the previous winter, again with no need to worry.
For those who may be interested, the trip to Spain produced an average fuel consumption of 23mpg - not bad considering a gross train weight of 5 tonnes!!
I hope this helps with your decision?