I've never had a problem with this.. the Sony takes ePub, PDF and text files, which is about the only file formats I have seen on the ereader book stores. I have heard from a friend who has one that the Kindle is a little fussier with which formats it likes and some do not display as well as they should (or at all).. but you can (I believe) get around this by sending the file to a kindle email address where it gets converted.. my reasoning to this is 'why bother with another step?'.. why not just have something that can read it all in the first place.
it also has Evernote build it (so you can keep track of any annotations and notes you might make) and evernote clipper so you can clip stuff online (yes it can connect to the internet with wifi - I never have though as I don't have the need for it).. same with the built in face book.. I believe with the newer ones you can also 'borrow' books from the library wirelessly (from home) straight to your reader too..
Hope it helps.. :)

