When Face Detection became the big buzz technology at PMA earlier this year, I, like many photographers, was skeptical. But I've been using the new Canon PowerShot G9 that includes Canon's latest version of this technology, and I'm impressed with how well it works for both focusing and exposure.
I like it because when shooting people candids; it's faster than my previous method of focusing on a person, holding down the shutter button halfway to lock the exposure, then recomposing. That method worked, but I lost good shots because it took a few seconds to execute. Face Detection is quicker, and using it enabled me to get more into the flow of the shoot.
What's really nice is that Face Detection also calculates exposure. This is particularly helpful for flash shots of people in low light. Typically cameras would overexpose the subject unless you used flash exposure lock (again time consuming). Face Detection knows what's most important in the scene and calculates the flash exposure accordingly.
Along with good image stabilization, I'm now updating my recommendatlon to include Face Detection as a "must have" feature on your next compact camera. It's the real deal.