$new_standard = strtolower("Twitter");
The immediate benefits are that any forward thinking Twitter client can now also be a WordPress or Tumblr client as well. Tweetie, one of the most popular iPhone clients, has had support for this for a while and immediately became the tool of choice for testing the new features out. Choices for users expand.
So, with that development aside, where next? I see three things.
1) WordPress should publish an official plugin for WordPress.org that enables the Twitter API for any blog. This act alone could create millions of possible twitter servers.
3) Everybody outside of Twitter should huddle for a brief second and add some new syntax to the existing twitter api that allows for a piece of metadata to be attached (urls to start), call it optional, and implement.
Or, in short– Now that you’ve shown how easy it is to implement Twitter’s API, rip it out of their hands, build a new community, and then market the hell out of it.