When I read questions like this one I wonder if we are aware of the fact that Academia.SE, and the whole Stack Overflow network, might be totally unknown to a large fraction of the academic world, especially outside fields like computer science or mathematics. And even if they knew, they might be totally unimpressed.
For instance, my nearest colleagues know about it just because they happened to look at my computer's screen seeing Academia.SE opened in the browser. And then the conversation typically goes like this (yeah, real kindergarten conversation from 50 years old people!):
Colleague: Academia? What's that, another one of your nerdy sites like [...]?
Me: This one's international!
Colleague: Ha! Academia?
Me: It's about the academic world: teaching, papers, PhD students etc.
Colleague: So, not only do you pester us and your students, but also them?
Me: Yes, you know that the main goal of my life is to annoy as many people as possible.
Colleague: I know, I know. But do they listen to you?
Me: It appears that I'm a top user... I'll probably even get a t-shirt!
Me: I'll wear it.
Me: I'll ask you to take a picture in the lab.
Colleague: Can't wait!
Hence, the titular question: do we have any data, even very rough, or general idea, on how much Academia.SE is known in the academic world? What is your impression?