Well - it's quite likely that the mobility side of things will fail before anything else, and thus the option to 'park' in an interesting spot is unlikely.

I believe the battery's are rated to 1000 cycles and are one of the major limiting factors. The dust deposition on solar arrays seems to essentially have gone away. Spirit is power-rich at the moment, Opportunity isnt too bad either.

In terms of longevity - I wouldnt be suprised to see us have issues with S1k ( Sol 1000 ) , i.e. the reaching of a sol number more than 3 digits long - which will screw up a few websites which list things as sol 015 etc. :)

The next rover on mars will be MSL in 2009 or 2011, so survival to then is very VERY VERY unlikely, but the next mars spacecraft is MRO, the high-res orbiter launching in August which will arrive next Spring, and if as a demonstration of the data path alone, it would be an amazing achievment to see MRO do some UHF relay from the rovers :)

Doug