Also remember that Kindle books are like Ipods, materials purchased are copyright sensitive (if you buy a USA book, it will vanish when you next go online in UK (or visa versa). A lot of stuff vanished from our e-purchases when we last arrived back in Trip.
I would suggest the Sony E-Reader, Superb, Accepts every format out there, not wifi or 3G so no worries about it connecting to the internet and policing your purchases.
The wife has one and swears buy it.
Me, I prefer a real book.
OB