Wired Magazine got an exclusive first look at the Di2 electronic shifting system by Shimano.  The new system includes two brake/shift levers, two derailleurs whose springs have been replaced by servo-motors, a 7.4-volt lithium-ion battery pack, and the wiring harness that connects everything.  The best part of the system appears to be its weight.  The Di2 comes in at 67 grams lighter than the Dura-Ace 7800.  Another great feature seems to be its auto-tuning:

The derailleurs, whose job is to move the chain from gear to gear as you shift, talk to each other and automatically adjust so the chain doesn’t rub. They also calibrate themselves, so you don’t have to play with cable tension to maintain shift quality as cables stretch and the chain and cogs wear. And although the control buttons have been placed in the traditional location behind the brake levers — so as not to confuse anyone or overly tax that mental overhead — they could be integrated with the ends of time-trial bars, the top of the handlebars or just about anywhere a rider might find convenient.

Previous attempts by Shimano, and Mavic all ran into a problem with power.  Mavic decided against even attempting to shift the power hungry front gears.  Shimano’s previous models and prototypes would only last upwards of 4 hours on a single charge.  It appears that Shimano has addressed these issues head on:

That wasn’t going to fly in a sport where grams can translate directly into seconds. The trick would be to conserve power, not squander it. Shimano’s engineers redesigned the geometry of the front-derailleur to amplify the force, so they could get the necessary output with far less input. The greater leverage of the new derailleur allowed for a much smaller battery and ultimately shaved half a pound off the system. Stetina claims the battery consistently lasts 2,000 miles between charges (which takes 90 minutes). Officially, Shimano says the battery will last for 1,000 kilometers (621 miles).

While they claim there is less maintenance, I have trouble believing it.  As one commenter on the Wired article points out, “If it’s electromechanical, it will fail. And chances are, it will fail in a way that you won’t be able to fix out on the road. One of the beauties of cycling is the conversion of human effort into motion. Distancing the act of shifting from human effort makes it inelegant. No thanks, I think I’ll stick with my old-fashioned Campy Record.”  Shimano will have to offer one hell of a package to get cyclists to fork over a 100% premium for an untested product.

Read the full Wired article here.