OK, so this is anecdotal, and we all know the plural of anecdote is not data...
I buy lots of books, and I can barely remember the last time I bought a book from a source other than Amazon. Even the used books I buy I get through Amazon's marketplace. About 2 months ago I finally broke down and bought a Kindle. I bought it to use on my commute, with the idea that I'd finally get around to reading all the classics (which are free), but would rather buy paper books for anything else.
Two months later I have been completely converted to the Kindle. I now don't even bother looking at books that I can't buy on the Kindle. It kind of sucks, as a lot of publishers charge a premium on Kindle books (how the hell do they justify that???), and other books simply are not available. But the convenience of reading on a Kindle trumps the disadvantages for me.
So for me at least, buying paper books is now a last resort.