re: How Long Can This Go On?!
Earlier this year, Squyres speculated at a public lecture when asked how long the MERs will last that Spirit would go for 800 to 900 sols while Opportunity would "never die."
Of course I think this was just before the dust sweeps off the solar panels and definitetly before Oppy met Purgatory Dune.
This is just another example of why certain deep space mission should be nuclear powered. The Viking landers had it and Viking 1 might have kept returning data until 1994 if a human error hadn't happened in 1982.