<p>I really feel that I should learn <a href="http://en.wikipedia.org/wiki/Lisp_(programming_language)" rel="noreferrer">Lisp</a> and there are plenty of good resources out there to help me do it.</p>

<p>I'm not put off by the complicated syntax, but where in "traditional commercial programming" would I find places it would make sense to use it instead of a procedural language.</p>

<p>Is there a commercial killer-app out there that's been written in Lisp ?</p>

complicated syntax
??
The syntax for lisp is
incredibly simple
.
Killer app written in lisp:
emacs
.  Lisp will allow you to extend emacs at will to do almost anything you can think of that an editor might do.
But
, you should only learn lisp if you
want
to, and you may never get to use at work ever, but it is still awesome.
Also, I want to add: even if you find places where lisp will make sense, you will probably not convince anyone else that it should be used over java, c++, c#, python, ruby, etc.