I consulted with someone working on an electronic odometer.  The
design was to use a microprocessor based system to write a somewhat
ofuscated pattern into an EEPROM.  The idea was to make the circuit
difficult to program arbitrary values into the EEPROM.  The
secondary purpose, acutally the primary purpose from the standpoint
of practicality, was to distributed the writes so as to avoid
exceeing the maximum number of writes fof the EEPROM being used.
The microprocessor also ignored pulses coming from the Hall effect
at a rate any higher than 110 MPH so as to make spoofing the reading
by bench pulsing at least somewhat undesirable.  This was for an
automobile that was not expected to ever exceed 110 MPH in
operation.  The case, of course, might not be the same for your
1993 RX-7!

The ECM modules of some cars do indeed store info about conditions
under which cars have been operated.  Since steering angle and
velocity data, etc is available it would not be difficult to
collect all sorts of interesting demographic information about the
drivers' use of the car.  I am not aware of any manufacturer
currently trying to enforce warranty restrictions based on reading
out use data from the ECM.  While it could be a potential invasion
of your privacy for manufacturers to have access to data about your
driving style, it could also provide valuable information from
actual field use conditions to help engineer more appropriate cars.
I personally wouldn't mind the dealer collecting my driving
demographics as long as it is done in an anonymous fashion.

