Been running dura ace 7800 with 7900 levers since March. Whilst I haven't done massive mileage, and while it is my second bike, training bike and winter bike, I have logged enough kms to give an assessment.
I am still having problems with the left hand lever when operating the front mech. It requires near incredible hulk force to shift to the big ring. LBS says that I should install a 7900 front mech or a 6700 but my colleagues who have the same combo have not complained about the same problem.
Refuse to fork out a cent more until the problem is solved by LBS.
Second issue is that it is only possible to downshift 2 cogs at a time whereas with DA7800 it was 3 at a time. Campy is about 5 if I remember correctly from my race bike. OK I can deal with 3 but it would be interesting to know why Shimano decided to restrict this on a newer "better" group.
( t is worth pointing out that I am running a pair of 09 Mavic Cosmic Carbo SL with an incredible aluminium surface which goes on to the next point>>
Braking is just not what I expected. Compared to others with their 7800 it comes nowhere near. Have tried it with HED wheels to with equally excellent surface and no joy so have had to fit swiss Kool Stop green pads. Braking is better but still not what I expected compared to colleagues' bikes.
I wish Shimano would introduce a group called 7850 with the best of both worlds: carbon levers with hidden cables, compact silver crankset, ability to shift 3 or even 4 sprockets at once, an extra click or two on the lever for front trim, and the possibility are having the new calipers in silver or at least a choice and even better, backwards compatibility like with 6700. Here in Barcelona where road riding is so popular, people have not come to terms with Campy 11spd or even DA7900. I have spoken to a lot of people on and off the bike and they are simply indifferent to the 2009 changes. Come on Campy and Shimano, you misjudged the market and we are in a world recession remember. I would love to see your sales figures for 2009.