I bought a Kindle a few months ago. (If you've forgotten, this is Amazon's e-book reader.) At first, I pre-ordered a second-generation Kindle, but after a few days, I decided to cancel that order and pick up a used first-generation Kindle, which was a bit cheaper.
It's a hard purchase to justify from an economic standpoint. For roughly $300, you can get books slightly cheaper than otherwise, and with less effort, and read them all on the same device. It would take forever for it to pay off monetarily, and even though reading a Kindle is a lot like reading a book - the print looks very good, it's not a computer-type screen, etc. - it's not quite as nice as actually having a book.
But I really like mine. It has led to me reading a lot more than before, because I always know exactly where the book I'm reading is, it keeps the page for me, and it's just a very consistent experience. I've bought a lot of really cheap books in the public domain (for around $1 each; you can get free editions but they tend to have more errors) that I wouldn't have bothered rooting around used bookstores for.
Also, I absolutely hate the way that books accumulate. I love books, love seeing them on my bookshelves, but hate moving them, running out of space for them, donating them to goodwill, etc. Even though I hate that all my books now look the same (like a Kindle!) and have no physicality, I also love that they are not physical objects taking up space in the environment.
Yesterday, Ed and I spent about 9 hours at his mom's house. Some of the time we spent moving furniture and equipment around, but most of it Ed spent rewiring a bunch of audio/video equipment, stringing wires through the crawlspace, etc. I spent hours and hours sitting around...with my Kindle. I finished one book and started another. And had I run out of books to read, or wanted a different book, I could have purchased one right off the Kindle at any moment.
I can't say whether the Kindle has been worth $300 or not (or whatever I paid for mine, maybe $250). But it's definitely improved my life and I've really enjoyed it. I would buy it again.