Steven Squyres talks about the long-lasting Mars Rovers
http://www.zwire.com/site/news.cfm?newsid=14155987&BRD=1395&PAG=461&dept_id=546876&rfi=6
They were only guaranteed to last 90 days and travel no more than 600 meters from their landing sites, but the two Mars Exploration Rovers (MERs), Spirit and Opportunity, have far exceeded scientists' expectations.
One year after bouncing down on the Red Planet, the famed robot geologists are still going strong on that distant world, traveling kilometers across the dusty surface and repeatedly confirming that in at least two places on Mars, liquid water once flowed.