The 3 main differences between gelato and ice cream are:
1- Gelato is made with milk, not cream like ice cream. This often gives gelato a more robust flavor than ice cream, as the extra fat from the cream in ice cream can dull the flavor in it.
2- Gelato is churned less than ice cream, so it has much less air in it than ice cream. This lack of extra air in it in return leaves it with a much denser/thicker texture, which often leads people to think it's creamier and richer than ice cream (although there's no cream in it! :P).
3- Gelato is usually stored at a slightly warmer temperature than ice cream, which makes it a bit softer than ice cream, (again making it taste richer/creamier).
Overall, gelato is nowhere near as prominent as ice cream, but is a very nice treat when available. If you havn't already tried this before, I would highly recommend you try it if you get the chance to. It's most commonly found in authentic Italian resturants. Gelato can also be made with water and alcohol (then called sorbetto) instead of milk.
Joe: Naw, let's try some gelato instead, it tastes a lot yummier!