Interesting article from The Association of American Publishers. Two things in particular struck me. People who got e-readers for XMas were still driving sales through February by "loading" their readers, which I gather means stocking up on books to read.
Also it looks like people who read ebooks are causing growth in the sales of backlist titles, because once we read a new book we like to read the earlier ones. All the more reason publishers should release their backlist for reasonable prices, we'll buy them, and they'll make more money.
http://www.publishers.org/press/30/