Readers here know I have my B&N Nook (see my initial hands-on and am very happy with it for several reasons. I wrote about the ability to load up and read all of my Fictionwise, eReader, Shortcovers, and public library content. I now have great news for those Sony Reader owners who are thinking about picking up a B&N nook, but don't want to lose all of their Sony Reader content. I have over 150 books on my Sony Reader 505 and today Sony launched new PC/Mac clients (renamed the eBook Store from Sony to the Reader Store) for managing your content and converted most all of their titles to the standard EPUB format. While this is EXCELLENT for people like me who have lots of purchased Sony Reader content, another part of this story is that people in Canada, the UK, and a few other countries can simply buy books from the Sony Reader Store and transfer them quickly to your nook with your PC or Mac.
I just redownloaded all of my books, fired up Adobe Digital Editions on my MacBook Pro, added my Sony Reader books to ADE and then transferred them to my nook. I cannot tell you how HAPPY this makes me since this lets me access my purchased titles and gives me yet another online venue to use for purchasing books. After transferring my purchased Sony content, I opened up a couple of books and they work perfectly on the B&N nook. The nook is turning into an even more capable device with a ton of sources of content.
I haven't purchased any books outside the US, but understand the Sony Reader store works at least in Canada and the UK. EPUB is really making some major strides in the ebook world and we now have support for this format on the B&N nook, Sony Reader, Astek EZReader Pocket PRO, and more (see the MobileRead Ebook Reader Matrix). Pretty much all ebook readers, but the Amazon Kindle are standardizing on EPUB.