Many people have a common memory problem. Associating the name and face. It is not rare that one fine day you meet someone you know and are left wondering her name. Also, a long lost friend sends you an e-mail and you try best, only to no avail, to remember the face. So when Riya introduced something like Face Recognition which (to the best of my knowledge) no one else has offered before, many people quickly caught on to it. It's a great service, a bit heavy, and I've never been so glad to drag and drop :)
It was great to know that Riya could identify Michaelangelo's David. It would be even nice if there were Riya communities or public forums like Keyhole community where users can upload such photos, recognize them and have some fun like what people do in "Where in the World" contest.