Got the tires about 8500 miles ago...immediately followed by a dealer alignment.
Initial ratings were almost perfect. I initially noticed that the steering requires larger inputs (not really a bad thing, just different) than the previous OEM ContiProContacts and my fuel economy stayed about the same with the Sumis. They grip the road much better than the Contis and my braking performance is also dramatically improved. They also grip well in the wet, but offer mediocre resistance to hydroplaning. I haven't reached the limits of the tire yet. I also like how they don't roll over on their sidewall like the Continentals. We had some minor snow in Charlotte and they seemed fine in the snow, also did alright on the icy spots.
After I rotated the tires, my steering seemed to wander a bit, so I went back to the dealer and got another alignment which they said wasn't necessary because it was still aligned. That did tone down a bit after 1000 or so miles, but then the tires started to cup on the inner and outer edge and they're very loud now. I expect them to last at least 40,000 miles, but I'm going to attempt an exchange as the tread is barely worn down (should still be under uniformity warranty). If I'm not able to get an exchange I'll just keep them as they're now only slightly louder than the OEM Contis when they were worn out (they were always loud). Also they are now pretty bad on rainy roads with hydroplaning. The tread pattern seems designed to push the water away rather than to pulverize and mist away the water. If I trade I'll try the Conti DWS tires more than likely. I would only get these again if they were priced at a give-away price, and then I wouldn't rotate them on my GTI.