I had planters fasciitis, too. My doctor told me I had because I was getting old and fat. He's much older and much fatter than me, which I was too polite to point out.
I found that hamstring exercises did a world of good. If you can find a Pilates book in your library, you'll probably find some great ones involving flexing your feet, things you can do at a desk even. As soon as I learned that, my heels began to hurt less and the pain was gone in a few days.