This plugin adds an admin page with some bar graphs with basic statistics from your BuddyPress installation.
The activities table structure will change in a future release of BuddyPress, according to Andy Peatling. However, the code in this plugin will be easy to adapt. Expect that a new version of this plugin will be out a few days after that change.
I'm also thinking about using the Google Maps API to create fancier graphs, such as pie charts for radio and selectbox fields or Venn diagrams for some multiselectbox and checkbox fields. You would then have to enter your own API key, though. If you think this is a good idea, say so!