With a high speed internet plan, where does the speed go?

I recently purchased the cadillac of Internet plans by me. On the speed test, I average about 38-39 MBPS and 5MBPS Upload. I am still deciding if this is worth it or not, aside from gaming, how do you capitalize on this speed? On P2P I am averaging only 1.5MBPS Download and 500k/s upload. When I download video from websites, its not much different than the basic Internet plan. 100k/s. Just curious aside from Xbox Live, where can I see the change.