As I have said in recent stories about short URLs, I believe that content management systems (blogging platforms, for example) should have their own short-link generators. Why hand over control of your traffic -- and your analytics -- to a third party, after all?
Automattic's Wordpress.com has launched just exactly this: its own built-in short-link generator. When you're creating a post on the Wordpress.com service, you get an option to create a wp.me link alongside the post's default link.
The big advantage to these links, over links from third parties, is that they are pretty much guaranteed to work as long as the Wordpress.com system lives. There's no additional point of failure you introduce by using one of these links. They're also really easy to generate -- you get a short link as you're writing your post.
Short links have been created for every post created using the Wordpress.com platform, which also means that the short links aren't as short as they could otherwise be. When I tried to get new short links for posts on my own blog, the identifying part of the link was eight characters long. New and sparely used shorteners create shorter links: Vb.ly is still creating two-character identifiers.
The Wordpress.com link shortener is "bespoke," Automattic founder Matt Mullenweg told me. "The whole point," he said, "is to couple the permanence of the shortened URL with the canonical one."
Mullenweg also said that Wordpress software users (as opposed to users of the Wordpress.com platform) can get access to the shortener if they use the Stats plugin. Update: That feature isn't available just yet.