What happened to Sophie's curse? During the movie, Sophie for the most part was seen in the form of an old woman, thanks to the curse the Witch of the Wastes cast on her. However, whenever Sophie slept, she seemed to revert back to her regular self. And when she was talking to Madam Soloman, her body was slowly reverting and her hair was changing colour. Also, when Howl was setting things up for everyone, her facial features and voice reverted but not her hair.

By the end of the film, Sophie still had white hair but she seemed to have regained her youthful appearance. However, the Witch of the Wastes never removed the curse, given her magic was drained. I am wondering if Sophie's curse was eventually dispelled or not.
The film glosses over the explanation with only a few hints, but it's explained properly in the original novel by Dianne Wynn-Jones (and its sequels). The Witch of the Waste's curse was only short-term, and wore off very early on. The reason Sophie didn't recover was because


   she herself had undiscovered magic talent, and was staying in the form of an old woman because she kept thinking of herself as such. She tended to revert whenever she wasn't thinking of herself that way - such as when she slept or when she was too focused on telling Madame Solomon off (and hence was thinking more of Howl).