Well, as everyone and their brother has been reporting, the DARPA race across the desert wound up with best showings of 7 miles (14km or so). Lots of coverage of the mechanical exoskeleton for soldiers as well.

Of course, coverage of Spirit and Opportunity has been phenomenal Still, they're expected to drive maybe a few kilometers in their entire working lives. That's not "fully explore a few square kilometers of the surface", but drive a linear total of a few kilometers (and that's an optimistic estimate, planned distance was 600m).

I'm thinking that practical robots for space exploration, and more importantly, development, will need to pursue the active-polymer path. There's some little bit of coverage for the electroactive polymers that are now emerging as useful tools here on earth.