amazon is local for me so using them at least contributes a bit to my local economy (though I mostly don't get books through them anyway but electronics & household items) but while I prefer to buy my books in local independant shops whenever possible, I do use Amazon for some of the stuff I can't find here.
Somewhat inconsistantly, I won't set foot in a Barnes & Noble or a Borders because of similar agressive policies that drive small bookstores out of business(and pathetically limited stock)