I just read an article helping hackers find the sweet spot on their driver.
The idea -- apply sunscreen to the face of the club and after you hit the ball, you'll see where you hit it. They call this practice tip "how to waste money on things that cost a lot." It's really practical.
Anyway, you can either put sunscreen on the face of your club or just use tape, which you don't have to keep applying and costs like $1 for nine miles.