Beam Me Up, Scotty!: The third ghost met by Scrooge is the ghost of Christmas Yet To Come, not the ghost of Christmas Future.
Memetic Mutation: This book is where we get the phrases "Merry Christmas" and "Bah, humbug", as well as people thinking that humbug is a term of derision.
He didn't invent "Merry Christmas" — it goes back to the 16th century — but he definitely resurrected it. They use both "Merry" and "Happy Christmas" in England (viz. the famous "Happy Xmas War Is Over" track by John Lennon and Yoko Ono, and Queen Elizabeth II 's annual message). "Happy" is sometimes preferred because "Merry" can imply drunkenness.
Money, Dear Boy: Dickens originally wrote it to pay off a debt. However, the story was a hit from the first release on. Dickens was also quite fond of the story and would keep revisiting it.
Saving Christmas: Surprisingly, this book did just that. In England and other English-Influenced Countries, December 25th wasn't celebrated as Christmas, or it was merely glanced over. Although Prince Albert married Queen Victoria in 1840 and brought over many German Customs for Christmas, the majority of the English Population ignored the holiday since the times of Lord Protectorate Oliver Cromwell, viewing it as too Catholic. With this Novella, Christmas immediately regained influence and prestige in England. The Commercialization of Christmas can also be attributed to this Novella, as the theme of giving to others, especially the less fortunate, was very visible in the book, and was what Scrooge learned to do at the end.
Not only that, but the book (and consequently Dickens himself) is commonly credited with inventing the phrase "Merry Christmas", which hadn't been used commonly up to that point. He didn't, but he revived it.
Word of Dante: Several details of the story have been used in so many stage and screen adaptions that it's surprising to learn that they weren't in Dickens' original. Belle is often referred to as Fezziwig's daughter, when no such detail exists in the book (in fact, many adaptions give her name as "Isabelle," whereas in the book she's simply called "Belle"). Also, the reason for Scrooge's hostility toward his nephew is never clearly spelled out, though most adaptions just assume it was because his mother died giving birth to him. Likewise, the reason that Scrooge's father is cold to him is never spelled out, but is often given a similar Freudian Excuse.
Word of God: At the beginning Charles Dickens speaks directly to the reader to impress upon them that Jacob Marley was dead to begin with. He explains this one fact is absolutely crucial to the story, and therefore warrants extensive Word of God confirmation, from death certificate to door-nail.