WordPress.com generated a shortlink for every post, as Matt announces and illustrates. It also generates a shortlink for every page. For example, this cute little URL will look like this: http://wp.me/xxxx.
This is good news, because the shortlinks will work as long as WordPress.com works: I think that’ll be a long time. I have less confidence in the longevity of small shortlink shops (such as tr.im, to which Matt refers in his post).
To conclude with a little buggy detail… The new feature shows up on the New Post page as a Get Shortlink button. When I clicked this button to get the URL, up popped a box with the shortlink nicely highlighted.