Had the issue with my RS4 that ultimately required a cleaning around 65k (covered under warranty since it threw a CEL). Bottom, line is that in the Q5, you'll likely not notice the issue unless you get a check engine light since the only thing most will recognize is a loss of power. Losing 15% power on a 420 HP engine is noticeable BUT on a 200 HP not so much. Ive read the best thing one can do to avoid CB is to avoid ethanol (Shell 91 doesn't have any) and push the car often as heating things up is good for it (gas consumption aside).