I measure everything.
Yes, even that. And that. Yes, and that too.
But what I measure most is myself of today against myself of yesterday.
I quantify my output and productivity regularly:
How many words did I write today?
How many emails did I respond too?
How many emails did I delete without responding?
How many working lines of code?
How many bugs squashed?
How much marketing? How many likes, comments, shares did I get?
How many visitors to each of my websites?
How many productive hours lost?
I find that putting metrics on a lot of different measurable aspects of my life permits me to figure out where I am wasting time, where I am spending my energy most productively, and where someone else is trying to consume it for me.