There is a gig we play in a semi permenant outdoor area next to a pub. A tthe weekend the guitarist was getting shocks through his guitar, but the worst one was last year when we were there when it had been raining, the guitarist sat on the floor which had a puddle on it, and then when singing got a shock to his mouth (which stopped him singing).
I have tested it with a tester, it says it is fine apart from the voltage being at 209V (and having 1v N-E), but it certainly isn't right there.