iPhoto 8.1.1 Update
A new update for iPhoto '09 was released today. It contains fixes for face recognition performance and accuracy, and also resolves minor issues with book ordering. The update can be installed via Software Update or through a standalone installer. It is recommended for all users of iPhoto '09.
WARNING:
If you imported photos of people while using iPhoto 8.1, there's an extra step you should take after installing the 8.1.1 update. Select all those photos, Control-click to open the contextual menu, and then choose Detect Missing Faces. This will re-detect the faces in those photos and correct any face recognition issues introduced in iPhoto 8.1. You should not quit iPhoto during the Detect Missing Faces process.
So far the update hasn't had any problems and is helping on performance stats a lot.
-NM