Depleted Cranium has a very nice new article on the Mars rovers, ending with this Curiosity graphic
With its RTG power source, the rover Curiosity will be able to spend much more time on the go and less time standing still. It will move faster and is likely to travel far more than thirty kilometers. That may well mean that the motors will degrade in a period of time faster than previous rovers. Of course, we still don’t know for sure. Furthermore, even if the rover eventually loses some or all mobility, it may still be operational for basic observations and measurements.
Even if Curiosity does not last as long as Spirit or Opportunity, it will almost certainly return many times as much scientific data, and that’s ultimately the important thing. The new rover is an amazing piece of scientific equipment, yet the amazing feet of endurance of its predecessors is none the less amazing.