With respect to JSP, JavaBeans are useful for maintaining state and for representing the information (the model) of your web application. You can use them to wrap up reusable functionality, although custom tags (also known as JSP tag extensions) are the preferred solution.
For a more detailed look at what JavaBeans and custom tags are useful for, check out
Chapter 8 (Tag Patterns) of Professional JSP Tag Libraries that is available to download for free.
Hope that's useful
Simon
[ September 26, 2002: Message edited by: Simon Brown ]