A problem I have come across before is when I want to include an image within a transactional email, using:
{{skin url="path/here/"}}
The problem being that by default, the transactional emails will look in the skin folder for the admin area in the base package. However if your storing images in the frontend skin folder for your package/theme, you need to be able to provide this CMS syntax additional information. You can specify the area, package and theme you wish to refer to. See the code snippet below:
{{skin url="path/here" _area="[frontend | adminhtml]" _package="[package name]" _theme="[theme name]"}}