The German Rail (Deutsche Bahn) offers rental bikes in major German cities. These bikes are placed anywhere in the city and you can leave them anywhere in the city. You only pay for the time you use it. This is organized by phone and with a electronic lock. This lock has an microprocessor and runs software. Apparently a wonderful target for hacking...
http://www.ccc.de/hackabike/index.html (English Version)
I especially like the "To ensure that nobody could discover our tampering by reading out the firmware again, we set the lockbit" part. :-)