I use the Bootstrap Toolkit for my apps now. For example, it's in the occupyweb.org project. Anyway, now that I use Bootstrap, I breeze through the UI of Twitter. I assume it's also using Bootstrap. If not, it's using something very much like it.
This is a D'oh moment. It was the thing that was wonderful about the Mac too, back in the mid-80s. A normal person could use five or ten apps, where on the IBM PC, the other burgeoning platform of the day, people were sticking with one. Having a unified UI meant people could do more with computers.