I've found this on A340s too - not just snorers, but laptop keyboard thumpers, laugh-out-loud-at-films people, through-the-night noisy chatters, and even those with their headphones turned up too loud seem to have more of an effect.

Still, that's what earplugs are for. At least it's more pleasant than the neighbours starting up drunken karaoke at 2am... Again...