NLP with Prolog in IBM Watson
cs.nmsu.edu
cs.nmsu.edu
(For example: http://lambda-the-ultimate.org/node/1867.)
Given that they switched from their own pattern matching language to an optimized WAM, I suspect they use one of the common Prolog implementations.
I liked the characterization of appropriate uses of Prolog: "excellent solution for the problem of pattern matching and all problems that involve a depth-first search and backtracking."
I have always longed to be paid to work in prolog since I was introduced to it in college.
Prolog as a culture is amazing; the depth of it, specially when it's submerged in other disciplines, like constraint logic programming.
But, standalone, as a language, by itself: it either forces your problem into a text-book toy exercise, or drives you to frustration. It does all the difficult stuff out of the box, but you will need to cut through it with a machete to accomplish the mundane.
I suspect that you have just used the wrong tool for the job. Prolog works well for problems that require reasoning, and unification extensively. But if you are trying to write, say, a parameter estimator in Prolog, you are using the wrong tool for the job.