This one was fun. I read an article in the most recent issue of Runner's World about tempo runs and decided Wednesdays would be an ideal time to put those into practice. Tempo runs are essentially designed to train your body to run harder for longer. Scientifically, this means you're increasing your lactic acid threshold. It's similar to drinking a lot of beer frequently except for the fact that tempo running is actually a good thing to do and alcohol consumption, while good in limited quantities, is nowhere close to as beneficial). If you drink a lot of beer all the time, your tolerance increases and it takes more for you to have the same effects you used to have with just one. With beer that's bad but with running that's good. You increase your tolerance so you can push harder for longer.
Here's how my first tempo turned out.