Before I could drive a car (after I got my license), my dad made me change each tire once and drive 1500 miles with him...best advice EVER.

Bike shops should not let customers leave the store without showing them how to change a flat--front AND back. It can be dangerous out there if you get a flat and are helpless.

There are lots of good links provided here, so please PLEASE learn to change a flat. Practice at home until you are comfortable with it. Take a class at a local LBS or REI if you have to. A little bit of self-sufficiency goes a long way.

Ride fast and have fun (and learn how to change flats!)