Carbon Buildup on valves and intakes is very common these days due to the Direct-Injection-fuel delivery systems cars are using to meet CAFE rules and MPG standards.

This method of injection is very precise and efficient since it delivers the necessary amount of fuel directly into the combustion chamber instead of running the atomized fuel over the intake valve and into the chamber. However, the fuel flowing over the intake valves cleaned them, such as the advertisement you've seen by major oil companies claiming cleaner valves by using their fuels. (Photo on the left).

TFSI Fuel Injection System as used by Audi and Other European Car Manufacturers