We have up to today put right at 7,200 miles on the Gates CDX system. I did replace the first belt at around 2,900 miles after we picked up some debris that caused the belt to come untracked. Gates suggested that I replace it as the carbon strands could have been stretched and if so the failure mode is catastrophic. The new belt has right at 4,300 miles on it and still looks great, the sprockets (belt rings) also still look great.
At this time I am happy with the system, it is clean, light and quiet and the belt is lasting as long as the chain. I hope that this second belt continues to perform for several thousand more miles. I have "0" plans of ever going back to a chain for the cross over drive.