Over the last two days I installed radiant barrier material in the attic over the garage. It's a pretty tough job being up in the attic space in the middle of the summer, I wouldn't want to do another one. However, I can now report that the radiant barrier makes a lot of difference on how hot it gets in the garage.
Since I am getting spray foam insulation put in against the roof deck over the conditioned parts of the house I needed to amend the attic over the garage too. I only punctured my head once, my back once, and gouged a hole in my shin while cutting a scuttle hole into the garage ceiling. Not too bad.