Yes, the authors I work with also use spellcheckers to help them, but they're not infallible, and Word sometimes switches back on you when you're least expecting it. I caught memorize in something my friend was pasting to me this morning, and her Word hadn't flagged it for her.
Also, there are some circumstances where two spellings are acceptable, but you'd use the word differently depending on the circumstances. In UK English, for example, everyday and every day are two different words with distinct meanings, but I notice in US English the first spelling is used for both.
