Yes, I have
I used it in desperation, as a last-ditch effort to untangle and save a clydesdale stallion’s mess of a tail. It had been neglected for a long time (just the tail - not the horse!) and turned into a combination of bird’s nest/dreadlocks. Literally, nearly the entire tail was one huge ball of massive tangles. And, it was a very, very thick tail, as you can imagine.
I had tried all conventional methods and products with no luck. So, before I cut it off, I figured it was worth a try with the WD-40. And, it worked great! 
I sprayed it in liberally and used the standard bottom to top detangling method with a sturdy brush. Although there was some breakage, the tail looked phenomenal afterwards. It took a while (maybe an hour or so of brushing) but it did enable me to get through that mass of hair when none of the other products could.
I immediately washed it out and then did the standard conditioning, show sheen, etc. to maintain it.
I wouldn’t use it for regular amounts of tangles or even winter dreads but if I had a last-ditch situation, I’d use it again.
Best of luck.