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That's right: WordPress has launched the WP.me short URL, designed for linking to your blog posts from space-limited sites like Twitter. It isn't a general purpose URL shortener or rival to Bit.ly: it's just for those on WordPress.com.
WordPress founder Matt Mullenweg writes of the launch:
-WP.me is the only two-letter .me domain in the world.
-Every blog and post on WordPress.com has a WP.me URL now.
-These are all exposed in the using rel=shortlink.
-It doesn’t work for any URL in the world, just WP.com-hosted ones.
-The links are permanent, they will work as long as WordPress.com is around.
-WP.me is spam-free, because we are constantly monitoring and removing spam from WP.com.