The source code formatting shortcode in WordPress.com blogs is nice and useful, but it's language support is limited. It would be great if you could just embed a GitHub gist, perhaps like this:
[gist 801520] or maybe
[gist https://gist.github.com/801520], or something, which would embed the gist right into one's blog, complete with source code highlighting for the much more extensive list of languages supported by GitHub gist.
Posterous users can do this by merely placing the gist url by itself on one line.