I spent about 30 minutes working with the applet and reading the accompanying textual material. The applet gives a good qualitative sense of the Fermi level and temperature effects on the occupation of energy states. The supplementary material is very good. The applet is simple to use and serves its purpose. It could be used as tutorial or as a lecture/demo. The supplementary material provides a clear mathematical analysis of the occupation of energy states and a worksheet for students to check their understanding. In addition, the reference section gives links to many other sources that will be of interest to students seeking more information.
I occasionally had problems bringing up a couple of the supplementary textual pages using Netscape 4.76, but no problems with IE 5.5.