Imagine a device that can be powered and cooled by the oxygen and blood sugar in human blood. It would permit the creation of embedded medical devices that would be nearly permanent. No need to change battery--just eat more!
Neal Stephenson covered this in The Diamond Age. People formed a massively parallel computer that performed computations in their blood stream with nanites and shared data between hosts via "fluid transfers."
They didn't quite solve the cooling problem though ;)
While I like your version more, I can't help but have certain scenes from The Matrix flash into my mind.