Joining the local lending library helped me a little on that score - at least it cuts down on the "I wonder if I'll like that" type bookbuying. Obviously works best for mainstream, classic or new books. They also have the advantage of selling on books for a negligible price when they've finished with them. Or take up reading obscure philosophical texts from the university library?

Never mind, as vices go, it's a pretty cheap and convenient one :-)