I tried iPhoto’s face recognition on the mac of a friend. It face recognition looks really promising. I find it an interesting feature in particular for for management of family pictures. But as a pity, iPhoto does not write it back to the images. This means, if one invests in it the data are threatened to get lost if a new image manager comes in to place.
As I use Lightroom, I would really like to see the same function in Lightroom or at least to see an option to transfer the data from iPhoto to Lightroom.