Just thought I would throw this out there - in a personal finance seminar I went to once, we were told that having a balance on your credit cards of 50% or so of the limit oftentimes leaves you with a higher credit score, than if you have several cards with high limits and no balances. The way credit scores are figured is pretty convoluted. Having no balances on your cards can leave you with too much "available credit" and make your score go down, because there is no proof you would be able to make all of your payments for everything on time if you did have to at some point use all of that credit.
Credit scores, as some posters have mentioned, are important for a lot more than just getting good credit. Most insurance companies now look at them, as do many employers. And having no credit does NOT give you a good credit score. My DH had never had a credit card, and his credit history consisted of about 2 items at the age of 35. His credit score was low, when we got married I had to put almost everything in my name because of that. I had him apply for a credit card and actually use it, and his credit score increased. When I got a new car, it was put in both of our names, and that increased the score more. Without actually using credit, when we went to buy a house our mortgage interest rate would have been higher because of his credit score.