Thank you everyone for your advice.
Liviu, the main reason I want the ereader is for portability. It seems much easier to carry than a hardcover book and I don't go anywhere without a book currently.
Interestingly, I own the HP Ipaq which has a Microsoft interface and never even considered using it for an ereader. It probably wouldn't work well though, as the battery life on it stinks! Plus my vision is getting worse and the larger size an ereader offers seems to be more appealing.