its a brand awareness campaign, by gareth posting it here, it being all over facebook, youtube...it has done exactly what it set out to do.
McD's hasn't got the best reputation brand wise, this is probably an exercise in brand personalising. It seems to be the big trend at the moment, look at the t-mobile adds, the fact that compare the meerkat is on facebook, twitter etc.
Plus it also ties into peoples urge for a few minutes of fame, this add will probably end up on TV at some point!
I like the idea regardless and yes the music is annoying.