My friend Elisia first showed me an ebook reader, the Kindle she bought as soon as they came out. The quality of the screen was jaw dropping - it wasn't anything like a computer screen, but instead actually looked like paper. As amazed as I was with the device, I had no intention of buying one. The form factor was clunky, it seemed like a superfluous device, and it couldn't natively display PDF files, which is the format I tend to read (and publish) in.
A couple months later I was wandering around in the Sony Store and I saw their ebook reader, the PRS-505. It had the same amazing screen that the kindle had, but was much smaller, less than a third of an inch thick. When I found out that it could also natively read PDF files I was tempted to buy it, but was still concerned that it was just a useless toy.
Six months later my friend Vince brought a Sony PRS-505 on the trip to Morocco that he joined me on. I found myself asking to borrow it constantly, just about any time he wasn't using it. If he fell asleep on the bus I'd carefully slide it away from his grip and read on it.
The final straw in my decision to buy it was the battery life. It uses no power to keep the screen on, and only a tiny bit to flip the page. All told you can read about seven thousand pages before you have to charge the battery. That's a good twenty or thirty books, which is at least a good two months or so.
The one advantage Kindle has over the Sony is the wireless book buying feature. This wasn't a big deal for me since I spend so much time out of the US, if I was someone who bought a lot of books and lived in the US, I might be tempted by it. On the other hand, the Sony is considerably smaller, can still read purchased books, and supports PDF.
Another big plus to the Sony is that you expand the memory with an SDHC card or Memory Stick. That allows you to carry thousands of books in a package far smaller than any normal book.
As you can probably guess, I wholeheartedly recommend the Sony PRS-505. I've had mine for less than a week and I've already read two books on it. It's really a pleasure to read on.
One warning: don't get the Sony PRS-700 without seeing it first. Unlike the PRS-505, the screen is a bit foggy.
Here it is on Amazon (ironically).