On the TutToaster.com site there's a recent post looking at using WordPress shortcodes, including how o style and implement them in your own site installation.

Wordpress shortcode API is a powerful function which was introduced from version 2.5, it's just a simple set of functions for creating macro codes in post content. If you've developed a Vbulletin forum before, you would have been familiar with the shortcode (something called BBCode) but the Wordpress users maybe not. In this article, I would like to show you how to create and use shortcodes, in addition, I will show you some creative examples of using shortcode in Wordpress blog.

They give a simple example of how to add a custom shortcode instance - a text call that displays "good morning" using the string "[gm]" in your content. From there they talk about adding attributed to the custom shortcodes and creating other special cases like custom lists, box styles, dropcaps, buttons, jQuery integration and a few more. All examples come complete with code samples.