So what's the difference between having cloud-based accounts and documents that sync between phone, tablet, and desktop? Then you can go to work and without even taking your phone out of your pocket (or even if you forgot it on your bed stand) you can start working with all your same stuff.

I believe Apple looks at the problem this way. Rather than have one piece of hardware act as all devices, they have multiple pieces of hardware that share the needed parts. (Though they haven't finished making it quite as useful as I'd like it to be.)

One of my concerns has been privacy. In this case what I mean is that I don't want Apple or Dropbox or Google or Canonical to own my data in it's cloud. I would probably be satisfied with a solution that only stored encrypted data in the cloud so that those data storage providers could not possibly access my data (so they couldn't be allowed to have my encryption key). I would also be satisfied with a way of hosting a cloud storage platform on my own servers (which would likely be a VPS, so I'd have to encrypt it anyway or else Linode etc. would have my data).

If we go the route of using the phone as the center, then we also need to add the capability into the Linux kernel to connect to external computing resources, like CPUs and GPUs. Then we're not limited to just a "thin client" type of desktop, but could have a full powered one.