Check this out: an interactive map of historic photos of now-demolished buildings in Portland. (I don't know why it is not centered!) Platial is a "social mapping" site where users can add photos and other items to an online map. A layer can be created by a single or by multiple users. Forsome other examples of how Platial can be used for interactive Web 2.0ish maps, see the Platial 2006 Map Awards.