Plug and Play -- Emphasis on Plug
I've developed a few embedded systems that were beyond the capabilities of a standard desktop computer at that time. But more often than not, my embedded systems were built not because a desktop computer couldn't do the job, but because a "standard PC" wouldn't be cost effective or would draw too much power, or simply wouldn't fit in the space required.
These days, though, there are lots of "tiny PC" replacements that are reasonably inexpensive, low power, and with small footprints. I've used the Friendly Arm boards, for example. Very small, nice mating LCD touchscreen and very inexpensive.
This morning the "Guru Plug" caught my eye. These are literally "wall wart" plugs that have a whole computer built in them. Gigabit Ethernet, 2 USB 2.0 ports, Linux, 1GHZ processor, WiFi, 512K of RAM, another 512K of ROM, Bluetooth, and U-SNAP (home area networking for devices -- I had to look it up). All for about $100 each. They have a slightly more expensive one that is even more capable.
The biggest limitation I see to these sort of systems is that they often don't include analog or digital I/O in the box which is a shame (well, the Friendly Arm does). That means you might need a USB or Ethernet I/O device (I was always impressed with the TINI and even wrote a book that talked a lot about it. I also designed some years ago a serial device that works well with a USB adapter that would fit the bill.
But I'd love to see a tiny PC-like module studded with I/O at a price that would make it practical for all but the most demanding embedded systems.