The ticked countries which can be clearly identified in Barney's world sex map are: Canada, USA, Mexico, Bahamas, Cuba, Panama, Colombia, Peru, Brazil, Iceland, UK, Ireland, France, Norway, Italy, Poland, Latvia, Lithuania, Russia, South Africa, Burkina Faso, Gabon, Kenya, Djibuti, Saudi Arabia, Pakistan, India, China, Japan, Indonesia and Australia.
Alyson Hannigan had previously played her own doppelgänger in two episodes of Buffy the Vampire Slayer (1997): The Wish (1998) and Doppelgangland (1999).
The title of this episode refers to the German word for look-alike. The word "Doppelgaenger" can be singular and plural in German. Anyway, "Doppelgangers" with a S at the end is NOT grammatically wrong in English; this is because "doppelganger" has been assimilated by the English language, and as such gets declined in English. For example, "pizza" has Italian origins, and the Italian plural is "pizze". In English (AND German), the word has been assimilated and is declined "pizzas".