Despite already having our own (week-long, springtime) holiday involving dressing up in costumes, Halloween has taken a firm hold here over the last couple of decades. Kids have never yet showed up at our door, but they're definitely out trick or treating.
I'd blamed chinese factories needing more places to sell their plastic halloween gear, but now it sounds like it just comes down to US media saturation?
Then again, we should all be stealing more holidays from each other; a more syncretic world is a less boring one.
[My german teacher in high school said the best thing about growing up in southern germany was that they got all the holidays (both protestant and christian) off from school]