There was a case a while back where a person was given a major fine for speeding in a rental car. The company (I forget who it was now) used the GPS system in the car to determine that the rentee was speeding and charged them some rediculious fee for breaking the terms of service (which states that you won't speed in the vehicle you are renting). Was overturned in the courts when it went to trial.
Also, more recently in Canada a guy hit and killed a pedestrian. The courts wouldn't let him claim it was 'an accident' cause the cars 5 second telemetry showed that he was going 157km/hr (98mph) in a 50km/hr (35ish mph; math done in my head) zone and didn't lift his foot off the gas pedal until after the impact.
On one hand, I'm glad they were able to put this guy away (for only 18 months though...) but on the other hand, the precident is a little ... er... odd. It doesn't directly set precident that the data can be used in court against you *arbitrairly*, but the fact that data from these devices was used to prosecute doesn't sit well with me. Though, this guy deserved it. He was convicted 3 years prior of a hit and run (property damage, no killings or whatnot) while going 3 times the legal speed limit.
More info from Slashdot:
http://slashdot.org/article.pl?sid=0...tid=158&tid=99