Less for me.
The majority of the books I bought were re-prints of old public domain books.
For newer stuff, I use the library. Heck, I'd probably use it for older stuff as well, but they don't really have anything before 2000 anymore, much less books from the 20s and 30s.
Besides, being poor, I simply can't ever afford to buy something on impulse. Every time I buy from Amazon it's either because I stop and buy a gift card, or trade in my change at a Coinstar for Amazon credit (no counting fees)