I see the Spark as a city car where the biggest threats are traffic and parking. A small car like the Spark can move easier in traffic, and find smaller parallel parking spaces that other drivers with larger cars will not dare try.
I had a 1968 Austin America that I drove for five years, including travelling to college and back with some roommates and luggage, yet as loaded as it was, it beat a Volkswagen in acceleration. At that time, it was fun to drive and used little gas (when gas was only 50 cents a gallon). Now I see thousands of small imports on the roads, from the Italian Fiat 500 and German Smart to Japanese Scions and Yaris. All are small cars that move well in heavy city traffic and can find parking spaces quickly. So the Spark will sell well for the urban short-distance drivers, and be a better vehicle than all the imports.
Really good quick explanation of what the spark is about. It definitely fits in with the rest of the compact and fuel efficient cars on the road.