You can use the face identification feature available in Picasa to name the faces in your photos. It will then search for similar faces and ask you to check if they are the same person. 

This can be quite useful if you have photos that you cannot identify, but know they have a family likeness and should be from your family lines somewhere. 

It can be a generation out in adding a name to them, but the full photograph itself will help you to add a date using the clues of clothing styles and the style of photographers logos and addresses.