Personally, I avoid deus ex machina like the plague - if you have to use one, it means you failed to set up the universe and the plot properly. It's like a whodunnit where there's no actual way for the reader to identify the perpetrator before the climactic reveal: there's no sense of closure for the reader.
Charles StrossFiction is about human beings, first and foremost. (It's not impossible to write fiction with no human protagonists, but it's very hard to keep the reader interested ...)
Charles Stross[Core concepts: Human beings all have souls. Souls are software objects. Software is not immortal.]
Charles Stross