When I was in high school, my math teacher would play Mozart during tests, claiming it would help us. It would drive me crazy, and I doubt that my grades improved as a result of the distraction.
For what it's worth, I have a BMus in Piano Performance. I love music... but never as "background noise"!
For really repetitive thought-free stuff (e.g. mopping a floor), music that I would listen to while just sitting down is fine. For less repetitive stuff, either something with a set pattern (like 8-bar blues) or something I know well enough to "tune out" when I need more focus on the task at hand is better.