So my recommendation is if you have the current one, stick with it. And if you don't have one, get one IF you think it would be useful. Because I do agree with Ace that the Kindle really isn't a mass market device.
...books are not precisely difficult to carry around, especially on the places where you'd read a book outside your home -- subway, airport, Starbucks, park. The Kindle is a bit thinner and lighter, but who's sweating the weight of a book?
For yet another thing, books are intrinsically pleasurable as objects. People like books -- the feel of paper, the smell of them. Kindle is not going to replace that attractiveness anytime soon.
But here's the big reason Kindle will never catch on, as a friend explained to me: How do you know what to read?" By which he meant -- without the pleasant ritual of going to a book-store, browsing the stacks, picking up a book and reading its back cover and first few pages -- how the hell do you know what you want to read in the first place?
These are good points. The Kindle hasn't replaced real books in my home or stopped me from browsing the book store. I like it because as a frequent traveler it allows me to carry around several books, magazines and newspapers in one compact environment. It allows volume for travel. So for people like me, commuters and other people who like volume in a small size it is great (especially for big tomes like Crime and Punishment).
But for my dear departed Grandmother - a librarian who read 4-5 books a week in the evening at home - she would be just fine without it.