Everyone does it because it is the fastest thing to have ready in the morning!

I make it too but just in summer. I love when it is so cold. In winter I still prefer traditional boiled porridge (warm and gooey :p ).
For the overnight one I always use oats, some extra oat fibers, flax seeds, nuts, sunflower and whatever other seeds I can find. In the morning I add yogurt and some fruits.
Yum yum :)