For me it would depend entirely on the book selections available - and then only as an eventual replacement for my Reader. I wouldn't throw away or sell an iLiad or Kindle if one was laid on my couch, but one reason I bought the Reader was to have a single eBook source.
At any rate I wonder if the Kindle did get Harry Potter exclusively, if that would be enough of a reason for some people. (And yep, Jon, I already know your answer to that.
)