I've been running a set on the front of my K8 along with Carbone Lorraine SBK5 pads for 5-6 weeks now and so far I'm very happy with them. Much less effort than stock(with EBC HH pads and Spiegler lines) with a good initial bite. One finger braking is the norm. Best looking rotor on the market, IMO, and a heck of a loss of rotating weight. Stock rotors weigh in at 3 lbs. 5 oz. each compared to the CTS rotors at 2 lbs. 4 oz. each. A total loss of 2 lbs. 2 oz. of rotating weight is pretty substantial. They wouldn't be my first choice for trackdays or hard canyon riding but for general street and dragstrip use they're great. I'll be installing the rear as soon as the pads get here.
I really don't know if they are or are not up to the task of extreme use but they do weigh only 2/3 of the stockers. If I was spending the coin on rotors for trackdays or such I think I would go with something proven to work and be reliable but to my knowledge these rotors aren't yet proven in roadrace type conditions. I think the great looks are getting them labeled as a "bling" part and racers are shying away from them.