The screen of the Reader, like the Kindle, isn't backlit. You'll need the same amount of light to comfortably read the screen as you would a print book. Incidentally, I finished reading The Mysterious Affair at Styles in the dark on the iPod Touch. Also, the screen is a bit darker than other eprint readers because of the touch layer. I like not having to arrow through menus or manage a bunch of buttons, but I'm not sure that the trade-off of less visibility is entirely worth it. Perhaps this is one of those things that I'll get used to (or will hopefully be improved in the next model).
As a librarian, I'm particularly excited to try out borrowing ebooks from my local public library's collection and being able to read them on my device. No other major ebook device manufacturer has that option (yet), mainly due to digital rights management and compatibility. Sony ebooks support several formats, including ePub, PDF, and RTF, and there's no charge to import supported formats onto the device, opening up the potential available catalog to everything but exclusive proprietary formats.
I'm still not a complete ebook covert, but between Scalzi and the potential of having a world of publications at my fingertips, I'm a bit warmer to the potential presented by ebooks and ebook readers.