Played with one at the office and was not very impressed. It can be useful in some areas: schools, hospitals in particular. It also comes in handy when traveling or reading something (though I prefer e-ink readers). But it should not cost more than 200$.
That being said I really have no intention of owning one personally. Considered getting one for my little sister's birthday but then remembered that she likes to play flash games
What are you going to do with it I wonder?