We (https://www.surveymonkey.com/) use it for all our services. I can't imagine using another framework! Pyramid is great for what we do.
I also know http://www.cars.com/ is heavily powered by Pyramid.
Shodan is a decently-sized website and runs on Pyramid (https://www.shodan.io). I don't know how popular it is in the general Python community, but it's been amazing to work with as a framework.
Now that I get it though, it seems like an interesting framework but not a productive one. I've only dabbled in Pyramid with my free time and have never built a serious project with it, but I can't imagine building anything large scale with it.
(I'm a .NET developer BTW, MVC is what I work with in my day job)