The mars rover website has a great article on how the spirit landed within 200 meters of its intended landing spot. Imagine, they sent this ship 300 million miles away and got within 660 feet of the target. Crazy. Read the article, very interesting. Here's an excerpt:

All the hard work paid off January 3 when navigators hit their target at the top of the martian atmosphere to within about 200 meters (660 feet), setting a new standard for navigation accuracy for all future interplanetary missions. "The trajectory was so perfect that not only was it within 200 meters, we also didn't need to adjust course in the final eight days of cruise," said Dr. Michael Watkins, navigation and mission design manager at JPL.