thanks for this plug in - we had it working great on a multisite install but something went wrong maybe 6 months ago.
One of the symptoms seemed to be very high site ids and probably duplication.
The site ids were up to 14000 odd - when there are only 100 sites on the wp network.
So i came back and reinstalled piwik on a new database (as the high number of sites was overloading it) and then upgraded to the latest wp-piwik and network deactiviated and reactivated and added the a new auth code for the new piwik install.
The immediate problem was that when trying to access stats from the dashboard it still remembered the old site ids. I guess this info is still in the database somewhere.
So i'm open to suggestions about to best proceed here. It would be great to get some help on this, let me know if there is more info I need to give.