You spend hours (…days?) making this great Flash intro file. What’s the use if a majority of your visitors do not have the Flash plugin? Do you know that (at the time of writing) more than 20% of Internet users do not have the Flash plugin?
When employing technologies that require the use of a plugin, make sure that you mention it at the top of the page and provide a link to the site from where the plugin can be downloaded.
SVG (Scalable Vector Graphics) and VRML (Virtual Reality Modelling Language) are two other important technologies that require plugins.