Sum of recurring contributions
In terms of an aggregation of actual contributions - in the contribution search (version 4.5+) it's possible to use recurring contribution dates in your criteria. The contribution search results page includes a total &amp; count.

That doesn't really answer your 'one membership should only be counted once' though. I'm not sure I understand that requirement. It seems like you only want to count one payment per person? If you only searched within a particular time period perhaps you would exclude the others?