We use it a lot - we receive requests of up to 5 M size of .Net structures, and just wade through all the strange class-relations with Prolog :)
I read that in 2014, 1/3 of all flight bookings in the word went through (Sicstus) Prolog.
It has its uses, and I like working in it :)
Agreed. I think this thought was the starting point of the http://cascalog.org/ project (a high level clojure frontend for Hadoop MapReduce).
I also use full Prolog to implement type systems.
Prolog extended with a constraint solver is another thing one may want to employ for an elaborate program analysis, see how https://github.com/eholk/harlan is using cKanren for its region inference.
So, in my book, Prolog per se may have very limited use outside of teaching, but an embedded Prolog or a dumbed down Datalog can be an extremely powerful querying DSL which can make LINQ look dumb and clumsy.