When you’re confirming or rejecting Faces in iPhoto, you can actually select a big ol’ group of images to categorize instead of clicking on each individually. If you know how to do it, it’s simple, but it’s not easy to figure out how.
So choose the Faces section of iPhoto to get started, and then double-click someone’s album to organize additional pictures of that person (the option for that is at the bottom of the window, labeled Confirm Additional Faces).
Then all you have to do is click and drag a selection box around the Faces you want to confirm, and they’ll get tagged as belonging to the person whose album you’re in.
On the other hand, if a group of images does not belong to the person in question, just hold down Option as you click and drag, and everything enclosed in the box will be rejected instead.
When you’re finished, click Done, and you’re…well…done. Not surprising, I suppose.