When you open a photo and click the "Faces" button, the program puts little frames around all the faces in the photo. In my 3 days of enthusiastic use, I would say iPhoto has found faces in 95 percent of the photos that actually contain faces. (In the pictures where it doesn't see the faces, you can draw your own frames.) The frames look much like those in the Facebook photo tagging feature - basically a white box around the faces.

It's definitely cool that iPhoto knows how to pick out faces in a picture, but the cooler part is that it can learn to recognize and distinguish between the faces.

Below each face frame is a caption box that, if you've already added someone, will list the person's name. If you haven't added the person yet, it will give you a box like this:

Once you enter the name, it puts the face and name in the "Faces" section of iPhoto (a cute screen that looks like a bulletin board with your people pinned to it). When you click on a person, it shows you a host of other pictures it thinks might be this person. You just go through it and confirm or reject each one, and iPhoto learns as it goes. Each time you confirm or reject a person, iPhoto suggests other pictures it thinks your person might appear in.

And, if you add a new picture to iPhoto, it looks at it and attempts to tag the photos for you:

Confirming or rejecting is, as you can see in the photo, as easy as clicking a checkmark or an "x".

Once you have people tagged, you can easily find all the pictures that contain that person, which is really handy.

The other great feature in the iPhoto '09 is the ability to tag the photos by location. If you have a camera with built-in GPS (they have these?!) it will auto-tag the location for you once you import the picture into iPhoto. Then you have a fun little screen like this:

You can click on the little pins to see pictures from those locations.

The only major "drawback" in my mind is that iPhoto doesn't recognize dog faces. I've tagged a bunch of photos with my dogs' faces, but when I open an untagged one, iPhoto doesn't recognize them as faces. I'm pretty sure that's an unreasonable gripe, but it would have been really neat to see it learn my dogs' faces.

I also still need to load some baby and toddler pictures of my son to see if iPhoto can recognize him at those ages. I'm betting I'll have to label a few of them and then it'll take it from there.

This is a really great piece of software if you like to organize things, like I do. But don't be surprised if you get sucked in. I've spent way too much time labeling locations, for example, just to see the little pins appear on my map, and I still have a lot to go. Thanks, Apple!

Check out the other cool features of iLife on the Apple site.