Clay wrote in Many-to-Many: Notes from ITP: Flickr-as-web-services edition:

“More importantly for social software generally, both the Flickr API and the inclusion of del.icio.us-style tags have turned Flickr into a service as well as a site. Both 24in48.org (24 people documenting 48 hours in NYC) and Bickr.com (photo contests) simply use Flickr as their back-end, as Flickr handles the uploading, tagging, and re-sizing, and has a fantastic set of APIs.”