To quote the book: "Adding manpower to a late software project, makes it later". There's some really good stuff in there, even for those of us that are less interested in management.
Some of Brooks' suggestions for the make up of a development team are interesting. In particular I have always liked the idea that there should be a toolmaker. Most of us are less efficient than we could be because we lack specific tools to do the job and we don't personally have time to make them. If we had someone who's only job was to make tools I think a lot of things could go faster. Of course this only applies to moderately large teams.
But I'm not getting paid for it, my manager doesn't order it. He's kind of happy to see us getting more efficient with less bugs. But it would be good to have some support.