Library or Bookstore?

I used to be a library gal, then after an impulsive purchase of every Sophie Kinsella book at this second-hand bookstore, I started buying books and stocking my bookshelves. The only reason I even made that first purchase was because of the great deal for books that didn't even look like they had been breathed on (I got 5 books for $20CAD, which is almost impossible to find since books in Canada are so expensive).

But then one of my friends asked me why I'd buy a book when I could get it for free at the library. The only reason I could come up with is that when I buy the book, it's mine: I can read and re-read it whenever I want to. Downside to buying books? Well, I keep buying them and never actually start reading them. So right now most of my shelves are filled with unread books and I just keep adding to that.

I'm still debating which is more beneficial: a library or a bookstore? O.O