The movie opens with Samantha Futerman (she's been in a couple movies in Hollywood) talking about a woman from France - Anaïs Bordier - who had contacted her because her friend said they looked identical ... and when Anaïs looked Samantha up online, she discovered they were both adopted and shared an identical birthdate.
They become friends online, and submit DNA swabs simultaneously via Skype. And before they have confirmation, Sam and some family and friends hop a plane to London to visit Anaïs. No one was terribly surprised when the DNA comes back and they find out they're identical twins. The movie follows them through their initial contacts on Facebook, to London, then another meeting in L.A., and then a trip to Seoul for a conference of Korean adoptees.
What makes the movie a success is Sam and Anaïs. It's not just that they're identical twins, but that they're identical charming goofballs. They're likable and I laughed out loud numerous times in the first half of the movie. I laughed less in the second half - not because anything bad happened, but there were less comedic moments and it becomes quite touching seeing them together as they learn about their differences and similarities and each other's history.
The movie has been very well put together: the music has a very upbeat, "Amelie" vibe to it, including one track that was a straight lift. It was weird to see some absolutely gorgeous location shots that had nothing to do with the twins thrown in amongst the often hand-held video shots of the two of them together, but they were beautiful shots, and the editing is excellent. All together a really charming experience, very highly recommended.
(In a similar vein, consider seeing "Meet the Patels.")