Embedded bluetooth systems
I have a bluetooth handsfree device, which occasionally gets into an annoying error mode, where my phone thinks the device is connected, and the device disagrees. Modifications to the phone's state - turning bluetooth on or off, powercycling - have no effect. The only apparent cure is to turn the bluetooth device off, and then back on again.
Unfortunately, it's the embedded handsfree system in my car. So I have to turn off the car, and then turn it back on again. My mother has the same problem - this seems to be a defect in the Toyota/Lexus integration. So if you're behind me when I pull out of the garage, and I turn the car off and on at the first red light, you'll know why.