Daniel Saffer has written a fine, useful, and readable essay on metaphor and its applications. This is great place to start if you are rethinking your teaching in light of the web. Below is a shortened set of his guidelines for using metaphors. Read the article to "fatten" the skeleton below. (You see? Metaphor is ubiquitous.)
Guidelines for Metaphor Usage
As we’ve seen, metaphor is a powerful but potentially dangerous tool for
designers. So how can designers use it appropriately? Some guidelines are
• Metaphors are cultural.
• Metaphors are contextual.
• Fit the metaphor to the functionality, not the other way around.
• Use metaphor to uncover otherwise hidden aspects of the material.
• Discard process metaphors when necessary.
• Don’t let your metaphor ruin key features.
• Choose metaphors that are appropriately scalable.
• Let your metaphors degrade and die.