Starting with GM and Audi in 1994, On-Board Diagnostics (OBD) has become vastly used and very popular in modern vehicles. The interface has become a standard for auto mechanics to measure, record, and monitor the internal functionality of the engine and other features of a vehicle. Up until recently, the only way to get a copy of the information in the OBD was to connect an expensive metering device directly to the interface port on the vehicle. But alas, as many of us carry pocket computers with us everywhere we go, we can now collect and analyze this information easily.
Thanks to Antuan Goodwin from CNET for his complete post