1. Lauren Weisberger, author of The Devil Wears Prada, makes a cameo as the twins' nanny.
2. Juliette Lewis and Claire Danes auditioned for the role of Andy.
3. Emily Blunt convinced director David Frankel that her character should be British rather than American.
4. The exterior of the Elias-Clarke building was filmed at the McGraw-Hill building in midtown Manhattan.
5. A Runway issue is displayed behind Emily's desk, featuring a cover with three models. It's based on the real cover of Vogue's August 2004 issue, featuring Priscilla Presley, Lisa Marie Presley, and Riley Keough.
6. Meryl Streep donated her movie wardrobe to a charity auction.
7. Gisele Bündchen agreed to be in the movie only if she didn't play a model.
8. One of the prop Harry Potter book 7 bindings used in the movie sold in an online auction for $586.00. The proceeds were donated to charity.
9. Valentino Garavani, who designed the black gown Meryl Streep wears in the museum benefit scene, is the only fashion designer who chose to make an appearance in the film.
10. The character of Emily was reportedly based on Plum Sykes, a writer and former real-life assistant to Anna Wintour.
11. Anne Hathaway prepared for the part by volunteering for a week as an assistant at an auction house.
12. Helen Mirren and Kim Basinger were considered for the role of Miranda Priestly.
13. When Andy is walking by the fountain in Paris and gets a call from Miranda, Miranda's name and number shows up. But if you look closely, the phone is actually showing an outgoing call TO Miranda, not FROM Miranda.
14. Meryl Streep's daughter, Mamie Gummer, played a Starbucks clerk in one scene, but her scene was cut for pacing.
15. Most of Emily Blunt's wardrobe is from Vivienne Westwood.
16. Thomas Lennon turned down the role of Nigel due to conflicts with his Reno 911! filming schedule.
17. At least $1,000,000 of clothing was used in the movie, but since costume designer Patricia Field had a measly $100,000 budget, most of it was borrowed.
18. Over 100 sets of twins auditioned for the role of Miranda's daughters.
19. On the first day of filming, Meryl Streep reportedly told Anne Hathaway, "I think you're perfect for the role. I'm so happy we're going to be working together," and followed it up with, "That's the last nice thing I'll say to you." And it was.
(All facts from IMDB.)