Shimano XTR Di2 is the first commercial electronic MTB shifting system. Yeah, we know it's expensive (we haven't nailed down pricing but expect it to be about $2500ish for the deraillers & shifters alone... ouch), but it's undeniably bloody cool. How does it ride? We don't know yet... the Shimano reps have given us very clear instruction to keep this demo system in the showroom, but bikeradar have a great video here.
Our first impressions are that it's very, very slick and smooth. The shift triggers require a firmer push than their Di2 road counterparts, and this is probably a good thing for mountain bikers. The rear derailleur always moves with pinpoint accuracy, and the front derailleur automatically trims to match - what's more, the FD even changes front rings automatically, following your custom mapping, so you can control the whole shifting system using just one hand (although you can override it with the LH shifter if you wish). We predict great things for Di2 in XC racing, especially in really muddy, grotty conditions where traditional cable mechs can seize up over the course of a race.
We've got this demo system in store for two weeks only, so come and have a look while you can!