I've had my iPad for about 3 months. I mostly use it for web-browsing, watching shows/movies and playing games. I got the 3G version, but only activated it for one month when we were on vacation. It was way cheaper than using the hotel's Wifi, and worked flawlessly. I turn it off when we're at home, since I have Wifi at the house, and I don't take the iPad when I'm out and about.
I've tried it as a book reader, and frankly, I'm not that impressed. Yes, the print looks good, but the screen is highly reflective, which doesn't work well in sunlight, and the iPad is too heavy to conveniently hold up with one hand for any length of time (as when lying in bed).
It's a lifesaver when traveling with small kids, because we could load movies, tv shows and games onto it (many of them free), and it kept the kids entertained while flying.
All in all, I like it, and would buy it again, but it isn't yet the perfect device. I'm glad to have the 3G option, since it's painless to sign up for a month of service if I'll need it, and then discontinue the service when I don't.