The first two scripts are fairly simple examples of what you can accomplish with platform/browser detection and dynamic HTML generation. Here are several other project ideas that use these techniques. You can implement them into your Web pages, which will give you a better understanding of the great stuff you can accomplish:
Use browser detection to dynamically create whole pages that are customized to work with specific browser versions.
Create a page that will gather all of the information contained in the NAVIGATOR object, and dynamically generate a table that will display that information to the user (this is very useful as a development tool).