Like everyone else said, cleaning up after creepers, Scaffolding, leveling land for building. I also use it to make crude mock ups of structures so i can get an idea of how they look. Then i replace the dirt with the material i like. This also makes it easier to build designs into the item without planning ahead of time.
digging 2x1 straight down and bring 64 stack of dirt to build up. BTW the ratio of me dying by digging straight down is 1:25 im not sure if i put that right so its every 25 times a dig straight down I die once due to digging
So what do you do with your dirt?