The new release of Picasa 3.5 contains some amazing if slightly scary face recognition. Picasa will now scan your photos for faces once you tag a face it's pretty good a labelling every picture where that face occurs. It works really well, though it does seem to get occasionally confused with siblings.
What's so scary? Well if free software can pick your face out of a photo graph and recognise you I wonder what high end systems are capable of?
You can download picasa, the free photo gallery and editing software from picasa.google.com/