I have a Nook (NOT the color version, just the basic black-and-white e-ink one). I have found that I love it for traveling and work (I have lots and lots of reading time at work), but at home I still gravitate toward paper books. I am not sorry I bought it. It's impossible to get stuck at work without reading material, as I can just connect to the wireless network, purchase a book and download it in seconds. Barnes & Noble has a stellar selection of e-books, many of them very cheap or free, and the Nook is compatible with several formats (meaning I can check out e-books from the library).
I think these days most of the e-readers are pretty similar. You can handle a Kindle at Target stores, and the Nook at Barnes & Noble stores (and the Sony at maybe Best Buy?). I just plain liked how the Nook felt in my hand, which is why I chose it (didn't like all those buttons on the Kindle).