A very simple thought, not of broad interest.  

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.  

We will see the same effect, I believe, on the web, when the user interfaces start unifying. Bootstrap is an important step in that process. It may actually become the unification.