In an update to last week's status report from JPL on some spurious reboots that Spirit suffered over Easter weekend, the mission has actually referred to "amnesia events" on the rover. An "amnesia event," they explain, is when, for reasons unknown, Spirit fails to record science data into its flash memory. There have been four such events on Spirit, the first on January 10, and the last three during the last ten days. They do not yet know whether the amnesia events are related to the reboot problem, which happened once last weekend and twice the previous weekend.
Although these events are puzzling and are not by any means good things, it is good news that Spirit's other systems are operating normally; the rover is power-positive and otherwise healthy. So they can focus on trying to solve the problem(s), or, failing that, to circumvent them, and not be panicking about the rover's state of health. The amnesia problem is serious enough, though, that they mentioned in the status report the possibility that Spirit's flash memory (which stores data even when the rover is asleep) may no longer be considered reliable, and that they'd have to switch to using RAM (which is cleared when the rover shuts down every night) for operations. This would have a pretty serious impact on how the mission operates; at present, data is often stored in flash for weeks or more and is downlinked according to its priority whenever bandwidth allows.
Meanwhile, on the other side of the planet, things are going well. Opportunity seems to have driven backwards and rested long enough to have redistributed the lubricant inside that worrisome right-front wheel; it's no longer drawing extra current. So the rover is now being driven forward again, alternating with backward drives. Recent drives haven't been terribly long ones for Opportunity, but the rover's made steady southward progress of about 300 meters in the last two weeks, stopping at a series of very small, very recent craters.
We know you love reading about space exploration, but did you know you can make it happen?
Consider a gift to our Space Policy and Advocacy program to fuel more missions, more science, and more exploration.