I got my Kindle on Tuesday, plugged it in as noted and waited for the charge indicator to turn green. Have been using it a bit, in the main to read the Indie, currently on trial. This morning, 3.5 days later, the kindle flashes a message that battery is extremely low and to charge immediately. Hope it gets better with use, I know they can.
This is with 3G on constantly, yes I know I don't need to.
On the plus side it's easy to hold and use even with one hand (dominant in my case) in a cast, which happened last Sunday after I fell off my bike!