Automatic Medium-Dependant Interface Crossover is a licenced technology from HP. According to their website at http://www.hp.com/hpinfo/abouthp/iplicensing/automdix.html 200million ports supporting the technology will ship this year.

Its not supported on all Cisco switches, & it prevents the wrong cable from being installed, eg a striaight through between two switches, by simply swapping the transmit and receive pairs if the wrong cable has been used.