There is no report that provides an administrator a list of all AAF users and as such we cannot answer the question 'who is using your application.' We need a report that allows us to pull all AAF users and a bonus would be information about their enrolled methods.
Perhaps no need for a report with the methods that are automatically enrolled (because everyone will be on it) but at least for the methods that are manually enrolled.
If having such report could be a risk, at least a report that shows the number of users enrolled for a particular method and this will help a company track the adoption rate of the method.
Another report that could be one that shows the number of users that authenticated using particular methods within a time frame. Perhaps an option to include/not include duplicates would also bring value to this report.