I have been often intrigued by the phrase "back-to-back". Referring to "back" is reminiscent of the rear of the human body.
I usually hear-
- back-to-back meetings
I see and use the phrase often as an American, and this cursory search of a UK news source shows it's common there too:
http://www.telegraph.co.uk/search/?queryText=back-to-back&sort=recent
It's common in both dialects and I've never thought of it as anatomical.
Americans certainly use back-to-back in reference to simple physical arrangements such as back-to-back seats in a railway car.