jspx extension indicates that the page is a well formed XML. This is
meaningful for the 2.4 Servlet Spec. A jspx page is also refered to as
a JSP Document, vs. a jsp which is a page. Another extension in the
mix is jspf, which is basically a JSP fragment that you can include in
the pages/documents.

Google around for more information on how to use these extensions, and
how they fit in the web.xml.

-cheers,
Manish

I believe the difference is that you have to use well-formed XML in
the jspx, where in jsp, you can do things like <a href="<c:out value="$
{url}" escapeXml="true"/>" title="stuff">link</a>

I could be wrong though, I only read about jspx, and that was quite a
while ago.