I would like to know how long my MacBook Pro was on today - total uptime for the day.
I just bought it, and I thought the battery was bad but it went on for longer than I thought. Of course, I wasn't standing next to it with a stopwatch... 
It would be a great feature for me to track time spent on devices anyways, to see which ones I spend the most time on. Maybe in System Report, or using a tool in Utilities? A script?

EDIT: I am asking this to do this on different computers, some built before 2011.