Can you hear the longtime Twitter users breathing out a collective "finally"? The micro-blogging giant announced that a list feature will launch soon. And it won't just be a feature on the main site, but it will also be added to the API (our Twitter API profile).
The ability to organize those you follow into groups is a long-requested feature. Though it has never been officially supported by Twitter, many applications built on top of Twitter have added it themselves. For example, Tweetdeck and Seesmic Desktop are two popular Twitter clients that let users maintain lists of users. There is also a recently-announced format, TweepML, that makes it easy to share lists, something that is also part of Twitter's Lists.
Twitter's feature will make lists public by default, providing new ways to discover followers by category (and follow all the members in a click). Private lists will also be possible, which more closely resemble how clients currently maintain groups.
Does the new feature mean that Twitter is making obsolete features in clients with groups? Unlikely. Instead, Twitter is formalizing the practice, as it did with replies and the retweet API. Once the lists API is available and clients have adopted it, a group I create in TweetDeck could be accessible from Seesmic Desktop and any other app with lists.