After discussing primary and secondary web buttons with a colleague, I came across an informative article from Sun's Web Application Guidelines. There are really good points and examples included in the body, such as:
"In some situations, such as where the user might lose a large amount of input data, present a confirmation alert before allowing a Cancel action. Also, when the meaning of the action is not clear, additional and/or different text may be used, such as "Cancel Wizard" and "Return to Wizard.""
7 Simple Elements