I was doing a Scholo-run (Or Strat, doesn't really matter) at the time the event was going on (So i was on the instance-server instead of the world-server), seeing almost my entire guild repeatedly get disconnected, then all quickly clamber online again, only to be disconnected again within seconds, that was one of the silliest things i'd ever seen, ironically, WoW can't handle truly massive events...
But on a smaller scale, any kill quest would become truly agonizing at busy times, layering is fine, seeing other people you don't interact with anyway mucking about in the background is vastly overrated.