Ever heard the saying "people are promoted to the level of their own incompetence"?

Yes, and its not just a saying, its called the Peter Principle. And according to Wikipedia, the official quote is: "In a hierarchy every employee tends to rise to his level of incompetence." I would have to agree with original beware comment. I also feel this quote from the Wikipedia article is also meaningful in this context and provides some additional insight:

"The employee's incompetence is not necessarily exposed as a result of the higher-ranking position being more difficult -- simply, that job is different from the job in which the employee previously excelled, and thus requires different work skills, which the employee usually does not possess. For example, a factory worker's excellence in his job can earn him promotion to manager, at which point the skills that earned him his promotion no longer apply to his job."