When I test drove my own smart, 7 miles on the odometer, I had a 2 second lag every time I hit the gas. If I didn't actually hit the gas, but let off the brake, it would inch up forward pretty quick. Now that it's learned my habits and loosened up 1200 miles later, none of that's a problem anymore. I let off the gas, it inches forward slowly. I hit the gas and it takes right off.
If the car's a demo model or has < 500 miles on it, trust that it will improve over time. If you buy one of those demos or one that has > 100 miles on it, the computer's probably got different habits learned and is doing its best to sort them out. With a few dozen hours of driving it'll learn your habits and smooth out.