I think e-readers continue to be more popular in the U.S. than anywhere else. Interestingly enough, us older folks seem to have taken
more of a shine to e-readers than younger people. Probably because the text size is easily adjustable and because that demographic is still the main readers of book in general.
I also agree with the lestatar above that e-readers don't tell the whole story. Cell phones and pad devices have to be factored in on the assumption that most folks would prefer not to have redundant electronic devices.