I prefer ebooks for the sake of portability, but I'm more likely to buy print books.

Simply put, buying an ebook does not confer the same rights as buying a print book so it has less value in my mind. For example: I cannot give away an ebook. This may sound like it doesn't add monetary value to a book, but it does so indirectly. I buy many of my books from used book sellers, mostly charitable organizations since they have very good prices. These organizations cannot sell books if people like myself don't donate books.

At the end of the day most of my ereading is done with library books, public domain works, and works that are freely available online (or at least offered at a price on par with print books from charitable organizations). I have a smattering of books from the big publishing houses, but the decision to buy those books was based upon the very high value of the content itself.