Did you know that you can use OS X symbol and text substitution for smart markdown substitution? It's almost like using TextExpander. You write a few characters and OS X automatically substitutes them for a markdown snippet.
Go to Language & Text in OS X System Preferences. Open the Text tab. Make sure the Use symbol and text substitution check box is ticked. Click on the + in the bottom left corner. Write your markdown abbreviations in the Replace column and your markdown snippets in the With column. Don't forget to tick the On box for the snippets you want to use.
This can be used for almost any text substitution you like. You can have xbr be replaced by "Best regards," and many other clever uses.