I'm just gonna put this right out there: I don't really much care for Amazon.com.
Yes, I've bought things from their website—loads of things, over the years. Books, even. If I sat down and added up the amount of money I've spent at Amazon over the past decade or so, I'd probably have a heart attack and die, so I'm not going to do that.
And they've done things to piss me off in the past. Remember that whole thing about them censoring queer titles from book searches? Yeah, things like that. Lately, though, I've been reading about a few really jackass maneuvers the company has made that they don't feel they need to explain or correct (although apparently a little bad publicity has caused them to restore the Norwegian woman's Kindle account, according to BoingBoing). From a public relations standpoint, they are not doing themselves any favors. From a digital rights perspective, they look like they're abusing their privileges at best, and thieves at worst.
I haven't bought a book from Amazon in I don't know how long. The censorship issue was pretty much the nail in the coffin for me as far as they're concerned.
When you go to the bookstore and buy a book, it's yours, that physical artifact. You can read it, lend it, write in the margins, put it under a dodgy table leg, however you like. No, you don't own the words as if you'd written them yourself, but the bookstore isn't going to come knocking on your door one day and try to take it back. And yet Amazon had no problem doing just that. No warning, no refund.
I can't tell you where you should shop for e-books any more than I can tell you that I think you're better off with paper books instead. (Besides, I have a Kobo, so it's not like I haven't read several e-books—usually slowly and painfully, but I've read them all the same.) I just think you're better off if you don't buy them from Amazon.
So, where do you buy your e-books? Do you worry about this sort of thing happening to your library?