I have been following this interesting space craft-gone-long-term-science experiment for a while. Since being launched 1972 and 1973 the Pioneer 10 & 11 doppler based location measurements have drifted off their predicted paths . This is known as the Pioneer Anomaly and may tell us something new about physics and gravity once understood. There are some recent efforts to understand this anomaly with terrestrial based processing power (also see note below on the file format issue), and some have discussed a whole new mission around solving it. Some more links below…

• New Scientist
  • “Slava Turyshev of NASA has been compiling additional data from the Pioneer 10 and 11 spacecraft that had been unavailable because they were in archaic file formats and storage media.”
• Physics World

UPDATE:  Looks like Turyshev’s data has yielded some interesting results that blames the uneven heating of the spacecraft for it’s drift off course.