Okay doubters, I detect that smirk on your face... I was one of you too.
This feature appeared to be just another gimmick to excite gullible consumers but now that I'm experienced I must admit it is pretty cool, particularly for those everyday group photos we all make of ourselves and our friends. Here's why it's compelling and how it works (Fuji's implementation):
The above photo shows a little 3-D cardboard display at the Fuji booth that simulates a typical group photo situation. As you can see, the face detection shows up as boxes around people's faces. Fuji's system detects up to ten faces. If people are moving a little, the system tracks them showing the boxes moving along with the faces. It's kind of eerie, really. Anyway, you're locked and ready to shoot. Easy.
Specifically, the photographer sees a green box on one face–the primary face used for exposure–and white boxes on everyone else. The green boxed face is metered for proper exposure and focus while the white boxed faces are also worked into the equation.
But, the feature doesn't end there. In fact, I think Face Detection comes into its own during playback. When you playback the photo you just made, Face Detection highlights all the faces and then enables you to toggle thru each person's face so you can see if they look good or not! Wow, no more squinting or painstakingly scrolling around the screen to see everyone's expression up close! Just click thru the faces to ensure they're all looking their best. Playing with this capability was fun and can make the whole group photo process more interactive if you chose to show the faces around to everyone.
Be sure to try this feature for yourself. It won't make you necessarily want to buy a new camera but when it comes time to get a new point-and-shoot, I'll bet you'll be looking for Face Detection. Then again, it will probably be a standard feature on almost all point-and-shoots eventually. Finally, no, we didn't get a chance to test this with any pets, but I am curious...