I love the blog and dread having the appellation 'nitwit' applied to me, but I must ask two questions regarding the publishing process.
Assuming a publisher buys the book, does the author have final approval over the galleys and cover art? Is this a typical negotiated item or do some publishers have hard and fast rules about this sort of thing?
This is not a nitwit question, sorry. You are eligible to try again next week.
Now to the answer: no and no.
That said, this isn't a face off with author on one side and design or editorial on the other. Everyone is aiming in the same direction: a well published book that will sell.
I've had meetings when the cover art made me faint dead away but I'm not a designer. Those guys know their job. They know what's passe, they know what works for the size of the book, and with the marketing department they are a hell of a lot smarter about what gets someone to reach out for a book and pick it up in the store than I am. They don't tell me what "fresh and original" is and I don't tell them how to design a book.
In other words, unless they spell my author's name wrong or want to give it a title that breaks the law, I'm not arguing too much.
Sometimes the designers lose their minds though and I have had a few conversations that start out "are you insane?" but those are really few and far between.
Most authors do not have cover approval in their contract. No one I represent does.
As to galleys, by the time we get to galleys we've gone back and forth on the text a lot already and everyone is as happy as an author ever is when told they have to quit fiddling with the text. If an author absolutely doesn't agree with suggested editorial changes, we find out LONG before we get to galleys. The only option there is buying the book back if the editor and author can't agree. I know there are certain "don't change a word of my text" authors but I don't represent them.
Remember though, this isn't adversarial. We all want your book to sell really well.