I've had one for about 18 months and am still very pleased with it.
The only negatives are that there seem to be more typos than in a normal books, and not all books are available in electronic form. Hopefully this will get better.
The battery life is great, provided you remember to switch the wireless bit off after downloading it. The books are a few pounds cheaper than a paperback too, and some are available free. Most classics can be obtained from the Gutenberg project free of charge for instance.
Amazon let you try reading a sample before you buy it which is useful, and if you make a mistake and buy a book you don't want it can be returned. It's rather easy to press the wrong button sometimes.
If you fall asleep whilst reading it, it too goes to sleep after a few minutes, remembering where you had got to so that when you switch on, you are returned automatically to the page you were on.
Be aware, also, that if you buy the £89 one, you don't get a charger. However, as it uses a miniature USB connection you can charge it from your computer if you have a suitable cable or buy a cheapo charger separately.
Good luck. Hope you like it as much as I do.