Here the great TonidoPlug, a small plug computer with embedded Ubuntu Linux serves as a personal cloud, but not for the iPad.
Files created on the iPad can't be emailed or uploaded to the TonidoPlug because the iPad lacks an exposed filesystem. Even downloading files is cumbersome. Luckily, GoodReader comes in handy. The Tonido folks at CodeLathe do mention OneDisk from the Readdle guy, to connect via WebDav, but I have yet to buy and test that.