I just learned a bit of it for a class in programming languages(paradigms, assembly(simple), prolog, haskell, perl) prolog is a bit of a pain to work with if the problem is mildly imperative in nature. It is very useful if the problem is or can be written in a declarative fashion. That's just my take on it from learning a bit of it for a class though. I am sure if you are a veteran at it you will be able to make it bend to might.
It's a bit like lisp was traditionally. You'll probably never find an employer that will allow you to use it. But it's worth it just to understand a new way of thinking about programming.
