1. Go to http://picasa.google.com/ and download Picasa 3.5 (not the 3.0 or 3.1 version.)
2. Tell Picasa to recognize people's faces in your collection of photographs.
3. When Picasa is not sure about a face, it will ask you whether a face belongs to someone. This is where you will spend hours. Very addictive.
1. I know that iPhoto '09 already has this feature, but I switched to Picasa 3 many months ago because iPhoto '08 was gobbling up my disk space. Whenever I made a small adjustment (like straighten, lighten, etc.), iPhoto created a copy of the original. Soon, I was running out of disk to store my photographs. Picasa is more forgiving in this regard since it only stores the commands that I want to apply to the original pictures, not copies of the pictures. Also, I didn't buy iLife '09 (in which iPhoto '09 can be found) either.
2. Picasa runs on Mac and Windows. Within 2 hours of installing it on my Mac, I told my wife and she got it running on her Windows machine. Since then, both of us have been classifying unknown faces like crazy.
3. Titus had a lot of fun clicking faces to help Picasa.