Active Shoes

These are kind of like Positraction Shoes (linkskiy), but with very important differences:

They are powered by the movement of your feet. I can think of a number of ways to do this, and you probably can too.

"Racing slick"-like sole for high-performance on hard, flat ground.

Three or so mov/e/able hard metal pins on very light springs sense surface type. If the ground is hard and smooth, all pins are pressed in to the same exact position when the sole touches down. If the ground is dirt, they sink in somewhat. Et cetera.

Small grippers move out for moderate terrain, but full-size retractable cleats are deployed for extreme conditions.

Small pneumatic pump adjusts the 'suspension' in the shoe for optimal performance/comfort ratio.

Pace sensor senses how fast you're going, and adjusts everything for the best response and grip on the surface. The faster you go, the more agressive the nature of the shoe's components (firmer suspension, better grip on surface, etc.).

Even though these are somewhat similar to Positracs, the pace sensor/tread adjuster combo, suspension adjustment and even the power supply, in my opinion, merit another idea.