I have spoken to several people on the IRC channel who say that tags are enough and that albums/sets/collections are unnecessary. However, the model that many online photo services use, including Flickr, SmugMug, and Picasa Web Albums, is that photos can be in multiple sets and sets can be in collections, and they can be tagged as well. Right now, using tags as a sort of stopgap measure for organizing photos into albums doesn't work so well with things like Flickr, because the "album" name is exported as just another tag. If a separate "album" or "set" feature is added in addition to tagging, integration with online photo sharing services would be much enhanced. For example, there could be an option called "sync with Flickr" that would simply export the user's entire photo library to a particular online photo service such as Flickr, preserving albums as sets and not simply setting their names as tags. This feature could be implemented through modification of the tag system to support different types of tags, so certain tags could be labeled "album tags" in addition to normal tags.