[AoyW] The PC Was Never All That Personal
By design, the PC is not a mobile computer. In order to accomodate the per-unit tax levied for Windows & Office, PC designers jam more and more electronics into the box, keeping price and power requirements high. The result is a desktop or luggable supercomputer, rather than a true personal computer, which by definition should be effortlessly mobile. The few vendors who have tried to build pocket-sized PCs end up with devices that are underpowered for Windows, and terribly overpriced (see OQO). PCs get denser, not smaller.
Low-power x86 silicon has been around for years, and for cheap. Leveraging it requires a lightweight software architecture, which Microsoft will not embrace outside the PocketPC. Mind you, the PDA, with its poor input mechanisms, is a PC accessory, not an alternative.
The architecture of the web—rendering & input on remote displays—will let power-constrained mobile computers become full-fledged personal computers. Offloading the screen and rendering logic to local PCs allows reallocation of power to application processing and battery life. By this scheme, you don't need to carry a screen device in most work environments, as PCs are ubiquitous. For on-the-road I/O you may carry one, in the best size for your immediate needs.
Handheld-to-remote-display is a perfect application for Bluetooth; Intel Research prototyped it over 3 years ago (see Web 2.5 Pocket Servers). Unfortunately, handheld makers don't grok the potential of web architecture, consumed as they are with building so-called smartphones to head off the threat posed by ordinary mobile phones.
Real pocket web servers will eventually appear—they've been technically feasible for several years—if not by Bluetooth, then by UWB. They will likely evolve from flash drives. Contemporary flash drives are already a plausible deployment vehicle for always-on-you web servers. You plug in the drive, your personal/peer-to-peer web services run directly from it, they hit the local screen and possibly others via Wi-Fi, and you unplug the drive to quit.
Web 2.0 technologies, particularly SVG & AJAX, fill two big gaps in the web model, and thus open the door to Web 2.5, wherein web services run from your pocket, wherever you are, whenever you need them.