Well there's two different versions. I got the smaller one, with a 6" diagonal screen. They also have a 9.7" screen, though of course it costs more and you start to lose some of the convenience of small size. Just holding it side-by-side with a typical paperback, I'd guess the 6" screen is roughly three-quarters the length of the paperback and about the same width.
For reading books, the screen size isn't a big issue, actually, since you don't scroll -- you press a button to "turn the page". There's a font button you can press to adjust the size that you're comfortable with reading, and then the text just reflows to fill the screen, so you can strike a balance between readability and however many times per minute you're flipping the page. I imagine this thing would be a big plus for those with fading eyesight who could use a larger font. The font size I find most comfortable has, I would guess, around 120 words on a page. Turning the page is very natural, just a button-click with your thumb, and doesn't feel like scrolling at all.
You can also read PDFs, but it's not quite as friendly. I have some screenplays on PDF, for instance, and the bigger screen would be nice. I either have to deal with a font-size that's maybe a step or two smaller than would really be preferable, or turn the display to landscape for a comfortable font size, in which case there is some scrolling involved.
You can do other stuff like blog reading and very basic web-browsing, but really it's a dedicated reading device and should be thought of as such.
Here are a few of the pluses so far:
- Library in your Kindle. There's sooo much public domain stuff around that you could read for years and never spend a dime. Twain, Shakespeare, Kipling, Dickens, Austen, Sherlock Holmes, etc have already found their way into my device.
- Searchable text!
- Instantly sample prospective reads. This is especially good this time of year when everyone's putting out their top-ten lists.
- On board dictionary. Put the cursor on a word and get a definition.