I've become somewhat obsessed with the faces feature in iPhoto. Currently, I have about 7000 unidentified faces in my library. I knock out a few hundred here and there. It's oddly satisfying, but I go to a lot of large events - events where a lot of people look familiar because they are regulars, but I don't know them. This makes finding faces rather cumbersome, especially since the method of ignoring faces requires the mouse. Everything else can be done with the keyboard. Plus, doesn't track repeatedly ignored faces, so the same faces keep showing up. Well, I've discovered a way to work around these cumbersome limitations.
Doing everything with the keyboard makes things go a lot faster. If you're using the Find Faces feature and skip faces you don't know (because you don't want to pause to use the mouse), the next time you click on Find Faces, you'll be presented with those same unknown faces over and over again. They build up and always get presented in the same order, so you end up spending a lot of time skipping them before you get to new faces.
To avoid this, just name all these unknown faces 'Unknown' (or some other word with an uncommon starting letter). Then all you have to do to ignore a face (once you've tabbed to it) is type a 'u.' After you've labeled a bunch, open the 'Unknown' face album and bulk-confirm all the unwanted faces. Now the next time you use Find Faces, you'll get right to the new faces.
A few other time-saving tips:
You can create a smart album containing unnamed faces, open the album and hit the info button, then start tabbing and naming. The photos with unnamed faces will disappear as you update them. This allows you to have a good idea of your progress.
Not naming a face when the person's name is on the tip of your tongue, can make them rather hard to return to when their name pops into your head. I find it useful to name them something like '?Alan's Wife' or some other memorable note. All such names will be at the top of your Faces album listing (because of the question mark), and you can change the name of all occurrences simply by renaming the album.
Let auto-complete do most of the work. Most times, the first few letters are all you have to type before iPhoto fills in the rest of the name. Note, iPhoto uses Facebook, your contacts, and your previously named faces for auto-fill, but it skips contacts' middle names and does not include nicknames.
When confirming faces, if you come across a different face that you know, you can right/control-click and name it. Plus, sometimes all it takes to remember a name is the context of the photo, but the Find Faces feature does not let you zoom-out to see the whole image. Yet, when confirming faces, you can unzoom/zoom with the switch at the top-right of the window. I find that the confirm-faces interface is a faster way to find new faces than the Find Faces feature and I was methodically going through each face album to find new faces this way before I discovered the smart album trick mentioned above.
[crarko adds: Faces is not a feature I use very much, but this might get me to start. By the way, sorry about the slow July. I've been on vacation a bit, and the hint queue is pretty bare at the moment. I'll be putting up a couple of polls related to Yosemite as we await the public beta. Things will probably remain slow until that release.]
Mac OS X Hints