The basketball footage was taken at the 6 November 2002 game between the Knicks and the Kings (the Knicks won 96-88).
Kate Hudson improvised plastering Matthew McConaughey with kisses during the scene where she introduces the new dog. This is why McConaughey looks genuinely surprised.
A lot of the scenes were improvised e.g. the scene with the "family album".
Andi's friends, Michele and Jeannie, are named after the authors of the book.
Much of the scene where Andie crashes Ben's "boy's night" was improvised. Kate Hudson had the idea to toss the platter of veggies at the guys seated at the poker table. Donald Petrie, the director, knew she was going to do this, the actors in the scene were truly surprised.
The dress Andie wears to the Warner Advertising gala was designed around the 84-carat yellow diamond pendant which she wears at the gala. It was designed by the film's costume designer, Karen Patch.
Andie wears a Harry Winston diamond wreath necklace with an 84-carat yellow diamond pendant (called the "Isadora") attached, valued at approximately $5,280,000 and a pair of 5-carat radiant cut yellow diamond stud earrings worth approximately $125,000.
Lana's dress at the Warner Advertising gala is by Chanel, and her diamond tiara is real.
Ben's tuxedo at the Warner Advertising gala was custom-made by Brioni.
There were an estimated $14,200,000 worth of jewels lent to the film.
The filmmakers used a loft in SoHo New York City, NY for Ben's apartment.
The Conde Nast office building was used for the Composure Magazine office building.
The Alexander Hamilton U.S. Customs House, in the financial district of New York City, NY was used for the Astor Museum of Art, where the Warner Advertising Agency hosts a gala in honor of the DeLauers.