I found my ereader (2nd generation Kobo) replaced the books I would buy to read only once. And so I've tended to try out new authors on it. I can also load epubs on it, which makes it awesome for reading downloaded fanfic. And it is light enough to hold in one hand, like a paperback. It definitely reduced my physical book buying.

I now have a blackberry tablet too, and it has further reduced my paper, because there's so many things (mostly work, but also knitting patterns) I can store on it as pdf files.