Been a lot of them reported on the interned that last couple years, and those are only the ones that found their way into the news. Whereas most of these barbarians live in desolate, barren areas I shudder to think about how many stonings take place that are never known to "outsiders". As the modern information age peels back the curtians of islam we are witnessing a throwback into mankinds dark, barbaric past.
I do not think there is much vigilantism in Saudi Arabia. If crime is extremely rare there, but crime is punished very severely. SA is a police state, as its Ministry of Interior keeps an eye on its people.