The ability to not only find a word, but also to replace all instances of it throughout. If I could select between replacing just within a scene, or a chapter, or a part, or the whole manuscript, that would be a bonus.
This is possibly the top of my wish list right now. As a fiction author, sometimes a character name changes. I know of at least a couple other authors who are writing memoirs and using actual names in the initial drafts, but will need to change the names to protect identities before they are done.
If I could simply tell Shaxpir to replace all instances of “Larry” with “Curly,” it would save a lot of time and tedium.