Although it is indisputable that Fanny loves all three girls and chose good professions for all of them (even taking their ages into account), Sophie notes that the most advantageous profession would be Martha's, Fanny's biological daughter. As a witch, she would not only be very well-off, but she would also meet numerous rich and powerful people. Was that pure coincidence or did she really want the best for her biological child?
Another possibility. Fanny believes that as the youngest of three Martha is destined for greatness and the others are not. So she pushes Martha towards greatness while she looks for stability for the older siblings.
Did the Witch of the Waste become like that because she was twisted to begin with and let the fire demon's power corrupt her, or was the gradual destruction of her humanity a natural consequence of using the fire demon's power for decades?
Sophie is extremely blasé about being turned old, it's not until someone reminds her that her life expectancy has been severely shortened that she starts to think it would be good to lift the curse. Though it's hinted that her initial lack of reaction is due to shock.
Same for when she finds out she's a witch and has been using magic throughout the book. Again, she's rather blasé and accepting. It's not until she thinks about all the random spells she cast that she starts to worry.
It's not a book that drips with it, but that very determined scarecrow stalking Sophie, absorbing a skull into its turnip-head so it can talk, "in a mushy voice", and taking apart Percival, makes for a surprisingly potent example. Even if he turns out to be a Soul Jarfor Wizard Suliman.
Also, just about everything having to do with the Witch of the Waste and her master plan.
Rewatch Bonus: A lot of past scenes are put in a different light once you find out in the last chapters Calcifer saw Sophie's curse and her magic power immediately, told Howl about it, and they were both hoping she could break Calcifer's contract; that Howl's flirtations with Lettie and Miss Angorian were both put-on for strategy; and that Howl is conducting a complicated, deceptive plan over not only the Witch of the Waste and Miss Angorian - who both have their own conflicting gambits - but over Sophie, the entire kingdom, and himself. Almost the only action of Sophie's he didn't predict was her being decent to Miss Angorian.
Broken Base: The fans of the original book, in regards to the movie. Some enjoy the movie as well as the book, while others are not a fan of its admittedly extreme liberties with the source material. Some fans have found a compromise between the two, combining elements of the original book (such as the John Donne poem that serves as a focal point in the book) with the movie's designs in their fan-works.
Counts as this for Miyazaki/Ghibli fans in general. About half think of it as a brilliant piece of art just like every other movie Miyazaki made, while the other half sees it as a convoluted, messy, dramatically cryptic failure. Critical opinion is less divided (apart from Roger Ebert's disappointment with it), and Howl has a solid 87% "Fresh" approval at Rotten Tomatoes. Miyazaki himself considers it his favorite of his films.
Canon Fodder: Why did Prince Justin get cursed by the Witch of the Wastes, anyway?
Esoteric Happy Ending: The curses on Sophie, Howl and Turnip Head are lifted, Calcifer is freed, the Witch of the Waste pulls a HeelFace Turn and the war seems to be about to end. Seems like a perfectly happy ending, yet one must remember this all happened shortly after an air raid devastated Sophie's hometown, likely killing all her relatives and friends there. Then again, there were clear evacuations happening before the air raids started, so it's very likely that said relatives and friends managed to escape before the worst hit.
Estrogen Brigade: Howl is probably the strongest contender for this out of all of Miyazaki's male heroes, due to his good looks as well as his eccentric and likable personality. That combined with a compelling female lead who spends a large chunk of the movie as an unconventionally adorable old woman (a condition that in no way invalidates her importance to the story, in fact only strengthens it), it's easy to see how this movie would attract women of all ages.
Hollywood Homely: Young Sophie. She seems to pretty much be the only one who considers herself homely. It's more of a self-esteem problem. It seems she turns old and ugly when she thinks of herself as ugly.
Just Here for Godzilla: Predictably, Howl is the main attraction for the movie, especially in the more recent years.
Signature Scene: Howl and Sophie walking on air above the city during their first encounter is likely the most well-known scene in the film, to the point that it's often been parodied in fanart using characters from various different series.
The Witch of the Waste post-depowering. Despite how hideously obese and aged she looks, her sweet, somewhat oblivious demeanor is endearing.
Heen the Dog. He's short, scruffy, wheezes constantly, and has what look like bird legs, but he's still a loyal, lovable old doggie.
Unnecessary Make Over: While it's not hated, the short, black hairstyle that Howl ends up with at the end of the film is less liked than the various hairstyles he takes on over the course of the movie. Blonde haired Howl is not only the most preferred by fans, but it's also the most recognizable of his various looks (combined with the pink, diamond patterened jacket and green jewel accessories) and makes up the bulk of his fan-art, followed by the Howl with shoulder length black hair.
Visual Effects of Awesome: The titular moving castle itself is truly an sight to behold and its clear Ghibli put in a light of time and effort into making it look as mechanically detailed as possible both visually and how it moves. Its especially impressive given that while the castle is CGI, it blends in so well with the traditional animation, that one may not even realize that it is computer animated.
The Woobie: Sophie, particularly when she's first cursed and constantly tells herself not to overreact, when it's clear she's overwhelmed. Then she leaves home because she doesn't want to be a burden. Then her mother sells her out without Sophie even knowing. Life is rough for Sophie.