Today, venerable photo-sharing site Flickr added a people tagging option as well. You can tag people in photos in two ways: by typing a person's name or email in the "People in this photo" section much like adding a regular text tag, or by drawing a bounding box on the person's face, similar to adding a photo note.
You'll get notifications in your Recent Activity stream when other members add you in a photo. You can also see all photos you've been tagged in from your Profile. You can also use Flickr's Batch Organizer to do a lot of people tagging at once, handy for power users who have loads of pics in the back catalogue they'd like to add people to.
Plus, it's nice that you can tag people who aren't actually members of Flickr. To do so, you'll have to enter their email address, and Flickr will send them a message asking them to confirm that they appear in the photo and are okay with being tagged.