Yeah - I met a chap at an openbase conference in 2005 that was using it for professional web-application development. I've been intrigued by the idea ever since. I'd be interested to hear more stories from people who really leverage it like this.

I use mathematica for general scripting tasks. It takes a little hackery to do things like use it in a pipeline and such: http://ai.eecs.umich.edu/people/dreeves/mash/mash.pl

All Wolfram's own web stuff is done in Mathematica.