Not only that, if you are a decent enough customer, sometimes the company will likely offer you a new interest free period every now and again.
A good few times I've phoned up Barclaycard and told them I have a big purchase and Im about to go get a card from one of their competitors to take advantage of interest free periods. I asked them if they could do anything, it obviously triggered alarm bells with them and they give me a new 6-9 month interest free window. Basically I have a card for buying big goods on, and my barclaycard who can be relied upon to give me the interest free window as long as I pay them the transfer charge - usually 2-3%.
Of course one day this won't work and I will have to go out and get a fresh card.