Most credit/financial folks say that when applying for a home loan that lines of credit, esp LARGE lines ($10,000 or more) with a zero balance is definately a bad thing. And to have even a $2,000 'emergency' credit card which has a zero balance and is never used isn't a good thing either.
I'm going through Dave Ramsey's class and he is very much against using credit for ANYTHING except the home... having said that, my father in law gets a brand new F150 every three years or so. The last two of the last three trucks he got, he was financed for 0% at 60 months. The last one he got, he had recently retired and was offered something like 4.2%. As much as I am against putting things like TVs and vacations on credit cards, if you don't have any credit cards and you've never paid off a line of credit, there's no way you'll be approved for a 0% 60 month loan. Anyone with a lick of common sense will tell you if you are approved for a 0% 60 month loan, do it. Then put what you would have put in interest into an investment... A 0% 60 month loan is actually cheaper than paying cash for the same truck.