[The new features][link] allow users to [post and read friends posts][wp] via Twitter clients such as Tweetie and Twitteriffic. This is very clever.
[link]: http://staff.tumblr.com/post/287703110/api “Tumblr Uses Twitter API”
[wp]: http://en.blog.wordpress.com/2009/12/12/twitter-api/ “WordPress’ Twitter API Demo”