Cheaper than Paper - When you consider that Kindle-edition books are often the least expensive format on Amazon, even for new releases, if you read regularly it's a no-brainer. But that's the simple math. There are lots of low cost or free books available. And most impressive is the new Prime Lending program. With a Prime membership, one can borrow relatively new best sellers for free (up to 1 per month). Figuring one does this six times a year at $9.99 each, that alone covers the cost of the device over a 2-3 year life. Throw in library borrowing, which varies by area but is fairly broadly available, plus friend book lending for up to 14 days, and there are even more cost saving options.
Convenience - When traveling with paper books, I always fretting bringing along a book I was close to finishing as then I would need a second as well. With the Kindle, I always have all my books in one place. I also find myself reading in places I otherwise wouldn't: At doctor appointments, having my car serviced, waiting in the car for someone. The Kindle is so easy to bring with me that I nearly always have it.
Special offers (Ads) - Because the special offers are limited to when the Kindle is turned off and the menu screen, it's not very intrusive. Also, I don't mind getting good deal offers right to the Kindle. Again, the 3G is nice here because I can act on it right then and there rather than waiting until I have a wifi connection. I figure I'm bombarded with ads on my TV, the Internet, and everywhere in between. So if it's something I don't care about, I just tune it out.
Touch - Based on my experience using family members Kindle 3s, it is a big improvement over the joystick if you do any text entry and nicer in general for navigation. It also just makes basic reading enjoyable and brings Kindle back up to the competitive landscape (B&N, Sony, etc all offer touch). The dual touch, not on the competition yet, enables pinch to zoom, very nice for PDFs and other documents. You can also tap on a word for the xray feature and look it up instantly. Plus that saved physical keyboard space results in a smaller device. One feature on the competition (rhymes with Book) is the physical page turn buttons as a non-touch option. I think this would be a nice add to the Kindle Touch so that one has the option to turn pages either through touch or side buttons.
On the negatives, this edition surprisingly does not include an AC adapter. It does come with a USB cable. Most newer smartphones come with USB AC adapters so it's not really a big deal for me. I also can simply plug in the included USB cable into a computer to charge and I'm good for what appears to be a very long time (haven't had it long enough to call but the claimed 2 months seems reasonable). On the bright side, I bet most people will make do without buying an additional charger, thus saving landfills millions of chargers over the next few years.