Joining late as expected. Thanks for starting the thread, @FuzzyCaoraDhubh. I've enjoyed reading everyone's thoughts.
I really loved this book. I drove my DH mad laughing out loud at it frequently. Uncle Matthew, his entrenching tool and his hatred of foreigners was very amusing, and I also enjoyed the bit when Lord Merlin visits Linda in Paris and claims that he has to wear dark sunglasses to hide his "kind eyes" from beggars!
Mitford is a witty and engaging storyteller from start to finish. As with many of our Rather Dated books, I feel it gave some insight into the limited choices women faced at that time - in this case, of course, very privileged upper class women, but who nonetheless were constrained by circumstances, class and gendered expectations. Uncle Matthew's belief that education spoiled women's natural charms was telling.
Fanny somehow survived her childhood and abandonment by The Bolter (I loved it that her family actually addressed her as Bolter!), and was obviously the most stable, contented and emotionally intact of them all - presumably the influence of Aunt Emily, and having had the chance to get an education.
I'm inspired to read more Mitford, that's for sure.