Lisp obviously is an advantage for the AI stuff, but it doesn't appear to me that Lisp is any faster than Java, C#, or even C. I am not a master of Lisp, but I find it incredibly difficult to understand the advantage one would get in writing business software in Lisp.

Yet it is considered as a hacker's language.

Why does Paul Graham advocate Lisp? Why did ITA Software choose Lisp over other high-level languages? What value does it have over these languages?

There are a few reasons I am working on becoming competent with Common Lisp.


Homoiconic code. This allows structured self-modifying code.
Syntax-aware macros. They allow rewriting of boilerplate code.
Pragmatism. Common Lisp is designed to get stuff done by working professionals. Most functional languages aren't, as a rule. 
Flexibility. It can do a lot of different things, all at reasonable speeds.
Wartiness. The real world is messy. Pragmatic coding winds up having to either use or invent messy constructs. Common Lisp has sufficient wartiness that it can get stuff done.


Arguably the only real reasons to choose against Common Lisp is that the standard libraries are dated.

I will go out on a limb and say that in the general case, syntax should not be an issue to a professional software worker.
