Bruce Dawson taught a 100 level class at the college I attended, it's been a while but I think the class title was something around image processing. The first or second assignment was to copy one image region into another, little did we know that we implemented bit blit.

After turning in the assignment the next class he grabbed one random assignment from the class and added some quick benchmark instrumentation and if I remember right then asked the class how fast we think it could run. The next 30 minutes was a total geek out on cache lines, prefetching, alignment and all the other dark arts of performance optimizations. I don't remember how fast he got it to go over the naive for loop but it was many orders of magnitude. There's a few classes that really stick with you and that was definitely one of them.