While the camera Connector Kit does provide a physical USB port, it is not yet clear the scope of devices that might be accessible to the iPad.
It is clear that there is not general USB support
For example, while the USB Camera Connector will recognize a Compact flash reader when attached to it, when a thumb drive with photos on it is plugged into the iPad it says "The attached USB device is not supported".
or 'device requires more power'. I tried it with a scanner in my library, thinking I could have a more portable checkout system, but alas it doesn't work.