Mark Dain
I'm using bootstrap at work to take a several year old web app responsive. I've found 80% of our CSS can safely be thrown out as Bootstrap offers far nicer looking controls, often using similarly named classes. For example, we have an alert class. After throwing out our CSS, suddenly the alerts look nicer. Some HTML has had to be rewritten but I find it's clean and should we want to move from Bootstrap, we're using better code than tables in tables so the transition would still be easier I think, although it would be years until we need to make a massive rewrite of the front end again.