First of all, I figured out that there's no 'it'. It's a portfolio of products ranging from image recognition as a service to on premise NLP and enterprise search. All these products have their own specific use cases, some of them have hardly any real world use cases.
What I've recently been doing is using NLP for document classification. It's the type of problem you can solve with many different solutions, but 'Watson' is the one we're using.