I think everyone's a little overly concerned about this issue. Hopefully, I can clarify a couple things and make everyone feel more comfortable about having this thing in their car. From my standpoint, I can confidently tell you the following:
1. When police document a collision with a report, it's not usually very involved. Most collisions don't occur in our presence, so we're simply documenting the opposing sides' account (and witness accounts) of what happened. We'll throw in the damage to vehicles, physical evidence (skid marks, debris, etc), and a conclusion of what we think occurred based on everything put together. Most of this service is actually a courtesy to the involved parties, but not required because no crime occurred. That's why it's called an accident. If data recorders are needed, the case is more complex.
2. Most police officers and investigators don't even know about data recorders in vehicles. Sure, the highway patrol may have some special training about vehicle equipment since they mostly deal with traffic, but unless the cop is a car nut (like me), they may not even think about it. Even I never really think about data recorders until I read this thread.
3. The only time I can think of where a date recorder might be needed by police, the collision would have to involve a felony (for example dui w/serious injury or death), PLUS there is still a suspect alive to be prosecuted. That data recorder may hold some evidence and would be obtained through a warrant, but I've never heard of this. Most fatal crashes are simple to prove without the data recorder, either by proving the suspect was intoxicated, or by determining excessive speed based on skid marks, witnesses, etc.
Oh yeah, and even if a data recorder was obtained through a warrant, the prosecution would have to subpoena a Toyota computer technician to testify to the meaning of its contents.
All in all, I think data recorders are rarely used. If anything, the increasing presence of Nav in vehicles would be more of a concern, if they hold record of speed and location for any matter of time.
Hope this helps.