I was taught *never* to fly overhead a parachuting site, never to do an overhead join at an airfield with a parachuting symbol, and to give them a wide berth at all other times. I'm horrified that people bimble about in the sky without checking for parachuting (and other activities, too).
But I have had "bad experience" of parachuting sites. On a jolly last year with another PPL friend, we called a parachuting site in the Cambs/Leics/Lincs/Northants area to ask if they were active. We were given a right royal telling-off on the radio for even thinking of going near. Since we were VFR on top of an 8/8 overcast at the time, that made me very uneasy. We flew 10nm South of them to avoid any risk of hitting any IMC parachutists.
It wasn't Sibson. I phoned the place when we landed, and got more abuse. Not "polite warning" - but downright abuse. My buddy was tempted to complain to the CAA, but in the end didn't bother.