Wirelessly posted (Mozilla/5.0 (iPhone; U; CPU iPhone OS 3_1_3 like Mac OS X; en-us) AppleWebKit/528.18 (KHTML, like Gecko) Version/4.0 Mobile/7E18 Safari/528.16)
No central file system. When the ipad is dock to iTunes you can drap n drop files to the specific app on the side menu of iTunes. If you want to take files off your ipad, there is an export button in iTunes.
Apps can tell the OS what files they support so for example, you get an email attachment, mail app gives you a choice of which app to launch to use the file.