Since I have obtained my ebook reader my library use has not really been altered except in the case for public domain titles. These I will know obtain from sources like Mobileread, where in the past I would check out paper versions form the library.

I love my Sony 950 for the ability to have stored in one compact and easy to carry device every book (presuming availability as an ebook) that I am currently reading, or expect to read soon. Other advantages include the ability to easily highlight text and add notes, something impossible to do with paper books checked out from the library (and also something I am reluctant to do in books I own). I also like (in fact need for mass market paperback books) the ability to increase font size to a readable level for ebooks.

So for any particular book I would like to read my priority is (assuming availability) ebook from Mobilereads > ebook from library > paper book from library > purchase ebook > purchase paper book. The exceptions are for books with important graphic or image content, then I avoid ebook format.