Flickr Smartsets
I have to say that I find the current concept of flickr sets quite useless. Other than having a more visual grouping I don’t see how a set really is much different than a tag. If you still want the grouping and do this by tags anyway smartsets is for you. This service is great! You can define rules and it will automatically update your sets accordingly. So when I tag picture with “apachecon” it will automatically appears in my “opensource” set. A very cool mashup.