Some groups just get that developers are the key. Flickr had a good service, but not much to stand out.  So what did they do?  They learned from Amazon, from EBay and Google. They built a rich yet simple API set, added feeds, made it public and easy to build to, and evangelized to the geek community.  The result?  Some really amazing apps.  Check out this one: type in any series of words and Spell with Flickr will grab live images of text from Flickr pools to create a montage. Oh and it's done in script. Nice.