I'm looking forward to the prospect of decentralization, people using a "buddy system" (or whatever) to send backup copies of their files to friends' drives... rather than DEPENDING on the free (or freemium or commercial) offerings of commercial entities.
Storage capacity is cheaper-than-ever, yet people have allowed themselves to be steered into using phone or tablet form factor computing devices having minimal storage, with no choice (no SATA or USB port on the device) but to "upload it and store it in the (their) cloud". Post raspberryPi, I believe we're only a device generation (or 2) away from personal ARM -based wearable computers. In that scenario, I do expect the "personal cloud" paradigm to shift toward wearable and /or home-based "personal server(s)".
In the meantime, OwnCloud seems to be gaining traction. But (I say) if ya gotta authenticate through THEIR server... what's the sense in that?