The first shipment of Di2 parts arrived at the shop a few days back. I've seen these parts on a few bikes before, and I even test rode them a while back but I hadn't handled them individually until now. The first thing I got my hands on was the shifters. Which are super light, they piratically feel weightless in your hands.
Overall the hoods themselves feel similar to their mechanical 7900 counter parts, the major difference being that the break levers don't move side to side, which I like. To shift you just press the textured button and hold it down for multiple shifts. The other lever works in basically the same way as the mechanical style shifters. With the exception of throwing multiple shifts, again you just hold the lever down in the shift position, no multiple clicks in one throw.
The front and rear derailleurs however feel noticeably heavier than their mechanical counter parts. The servos (tiny motors) account for the extra weight. Shimano claims that the weight of the complete Di2 set up is the same as Dura Ace 7800. After handling the front derailleur, the rear derailleur, and the battery I don't see how this is possible but I'm in no position to dispute their claim. Of course if your a true weight weenie like me (I don't even have a computer) you'll opt for 7900, Supper Record, or Sram Red. But if your the kind of person who only cares about quality of shifting and you don't mind having to charge your bike, then this might be your sort of thing. Keep in mind though, this stuff is insanely expensive. The rear derailleur is something like $900. If you have to ask about the price of the whole kit, then you clearly have no business buying it. Also the battery and the servos will need to be replaced. And they don't last that long either. I think the servo life expectancy is something like 15,000 miles (I'm not positive on that exact number). While that may sound like allot, consider this: if you ride 200 to 300 miles a week, thats about a year. And yes as you might expect those damn servos aren't cheep. But hey, if you've got more money than sense your not really worrying about that type of thing.