I just hooked up an external USB keyboard to my tablet! Important thing I learned: get the correct USB adapter. You need a USB OTG host mode adapter, not a normal USB connector. The correct one is typically a standard USB female on one end, and micro USB male on the other, with some modified wiring of pins 4 and 5. USB host mode support was included in Android 3.1 and later, so external keyboards might not work with older Android versions.