some general questions about the tablet before i buy?: does the internal memory of the thrive affect how many programs you can install? on my phone, you only have so much room to work worth, so that limits how many apps you can install, unless you can move some of them onto your SD card (but not all can be moved..). would this affect anything, or can I just upgrade and use external memory (sd card) for this? Can you use a USB hub, to go from one usb device, to multiple? Is there a limit to the size of an external hard drive that it can read? what does it come with? what os does it run, and is it upgradeable? Is the screen scratch - resistant?