The plum-colored caped coat and matching hat Barbara Leigh-Hunt (Lady Cumnor) wears to visit the Gibsons is the same costume Claire Skinner (Fanny Dashwood) wears to travel to Norland in Sense & Sensibility (2008). The hat is also worn in Byron (2003) by an extra at the London party where Byron meets Annabella Milbanke.
The gold v-neckline gown with brown trim worn by a guest at the Easter Ball is the same costume Susannah Harker (Jane Bennet) wears at the Meryton Assembly Ball in Pride and Prejudice (1995), and Samantha Bond (Mrs. Weston) wears when Emma sings with Frank at Randalls in Emma (1996).
The blue striped dress with long sleeves worn by a guest at the Towers in the opening scene is the same costume worn by Gwyneth Paltrow (Emma Woodhouse) at Hartfield in Emma (1996), and by Mali Harries (Ann Rood) for her wedding in Byron (2003). The same costume is also worn by one of the maids at Chawton Cottage in Miss Austen Regrets (2008).
The tan striped gown with teal scallop trim at the hem worn by a guest at the Easter Ball is the same costume worn by Greta Scacchi (Mrs. Weston) in the final scene of Emma (1996), and by Emma Pierson (Fanny Dorrit) to visit Mrs. Merdles in Little Dorrit (2008).
The trivia item below may give away important plot points.
Molly Gibson replies to Roger's marriage proposal: "Yes. Yes I will. Yes." This is a direct quote from Molly Bloom's soliloquy in Ulysses by James Joyce, the last line in the book: "Yes I said yes I will Yes." Note that this is the screenwriter's contribution, because Mrs. Gaskell hadn't completed the last chapter.