Since I always find myself wanting to charge about a million things at once, I found a very small powered USB hub with an equally small wall wart, and use that to charge music player, PVP, phone & camera.
If you're going to experiment with the USB connector, I found a great little USB power cord: USB passthrough on one end, cable carrying power only ends in a universal socket with lots of little adapters. You could insert the cord into the USB port and still be able to use the keyboard.