The new firmware for the Sony Reader (model PRS-505) supports EPUB and Adobe Digital Editions. From MobileRead:
I can now confirm that this particular speculation seems to have proved out: the new firmware (available sometime today, July 24th) will include support for both epub and Adobe’s Digital Editions. It will also include support for PDF reflow, which is something we’ve long been looking for. As an extra added bonus, the new firmware will support DE’s DRM system for both epub and PDF. However you may feel about DRM, this support for it, along with PDF reflow, means that all those PDF e-books available from many public libraries are now in play on the Reader for the first time, so dust off those library cards, folks!