Paper on extensible languages
Slashdot linked this article Extensible Programming for the 21st Century this morning. As the author Greg Wilson points out, Lisp languages have provided features for many years that exceed those of new XML based languages.
There is an old saying: People who do not know Lisp are doomed to reimplement it.
I do use Common Lisp (e.g., my commercial KBtextmaster product).
I would use Lisp for most of my projects, but my customers almost always ask for Java (which is OK, because of the wealth of free class libraries and infrastructure code for Java).