Specifically, Aigner is bothered by the idea of Facebook providing user data to pre-approved partners. According to a translation of her letter provided by Spiegel Online, she stated, "Personal data is not allowed to be automatically passed on to third parties for commercial purposes without consent."
We should perhaps note here that this isn't the first time Aigner's complained about an American tech company's attitude towards privacy; she's in fact been one of Street View's most vocal opponents in Germany. And Google's still moving ahead with its plans to introduce Street View in Germany, so Aigner's uneasiness may not have many significant implications.
Still, Aigner - who's used Facebook enough to accumulate around 1,900 friends - did tell Zuckerberg, "Should Facebook not be willing to alter its business policy and eliminate the glaring shortcomings, I will feel obliged to terminate my membership."
Hat tip goes to Robin Wauters.