Incongruity
For a show as steeped in 1960's realism as Mad Men, It was jarring to hear The Infanta by The Decemberists at the opening of the sixth episode of season 2. Seriously? I mean, I know the song itself sounds like it COULD have been performed and recorded in the 60's, but it took me out of the atmosphere within the first 30 seconds of the episode.
Maybe people who aren't familiar with The Decemberists wouldn't even notice? But I did.