There is growing interest by digital collection providers to engage collection users in interacting with the collection (e.g. by tagging or annotating collection contents) and with the collection organizers and other users (e.g. to form loose "communities" associated with the collection). At present, little has been documented as to the uptake of these mechanisms in specific collections, or the range of behaviors that emerge as users bend existing facilities to their own needs. This paper is one step in that direction: it describes the social information behaviors exhibited in a cultural heritage photography collection in The Commons on Flickr, and suggests implications for digital library design in response to these behaviors.