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An earlier comment mentions the woman on the park bench next to Rachel and Marcus reading the book "Something Blue" by Emily Giffin, the sequel to the book "Something Borrowed". This woman is Emily Giffin herself!
Kate Hudson (Darcy) and Steve Howey (Marcus) also played a couple (who got married) in Bride Wars (2009).
Adam Duritz from Counting Crows has said he never approved the cover version of his song in this movie.
Darcy and Dex's wedding invitation says the wedding is at The Plaza, which is the same place that Kate Hudson and Anne Hathaway's characters vie to be married at in Bride Wars (2009).
Hilary Swank was cast but dropped out. Ginnifer Goodwin later replaced her.
When Dex shows up on Rachel's doorstep and the delivery truck is blocking her view of him, the truck is FedEx, but the only part visible shows "dEx"
Emily Giffin: sitting on a bench next to Rachel and Marcus reading the novel's sequel on which this film is based, "Something Blue"