I strongly recommend storyboarding for those creating multimedia products, especially interactive movies and web sites. Storyboards began as a visual aid that Hollywood uses when it lays out a movie, one sheet for each basic scene. Each sheet shows a sketch of the layout of the scene and gives information about what is happening in the scene and how the scene fits in the movie. More recently, storyboarding has been adapted to non-linear production. I offer on the next page a template that you can print and photocopy for use in storyboarding both Flash movies and whole web sites. As you can see, the page has a place for a sketch of the scene (slide, keyframe, web page, what have you). Ideally each such scene has a Title (as slides would in PowerPoint). Then it's worth thinking through what the Purpose of that scene is in the work as a whole and crystallizing that thinking in words. Next, knowing that purpose, you should make explicit what Content is needed in that scene (on that slide, on that web page) to meet that purpose. (Remember, Content can be passive for the user, like a picture, or active, like a drag-and-drop game.) Finally, you need to indicate what Navigation functions in that scene, both persistent navigation (e.g., there might be a home button on every web page in a web site or a next and a previous button on every slide in a linear Flash presentation) and local navigation (e.g., there might be links for items mentioned in the content or breadcrumbs to let the user go up a level in a site). When storyboarding linear work (e.g., a theatrical cartoon), you lay out the storyboard sheets left-to-right-top-to-bottom just like reading a book. When storyboarding a non-linear work, like many Flash movies and virtually all web sites, it is helpful to lay out the sheets according to depth, that is, the top-level sheets should be laid out left-to-right in a single (sometimes very wide) row, the next deeper level should be laid out left-to-right below the first sheets, and so on. It often helps to have a master sheet, too, that shows what sort of stuff (content, purpose, navigation) goes on which level.
Experience tells me that storyboarding works, so I recommend it highly.