6 years ago, in a pizza restaurante with many developers on Barcelona I said we needed a Bootstrap project. I said we needed this as a foundation to develop things without to deal the countless hours of fixing vendor stuff, calculating things and such. Everyone looked at me annoyed.
I remember one guy said to me "that's for gays". "A developer must do all from 0 or he will not learn". And also "I don't need that kind of help".
6 years later I created over these years around 5 HTML/CSS frameworks using the same patterns, maybe changing the classes names to avoid propietarie code jealousy and all the yada yada. I did what Bootstrap is, over and over again.
Now I use Bootstrap when I start a new project. I know Bootstrap like if I've made it. I have no regrets of this. The framework is friendly named, it's well documented, maybe it's a bit over designed (I have to kill buttons styles over and over) but in the end it's a solid foundation of semantic HTML with cool LESS stylesheets.
We can argue many things about frameworks, but in the end, HTML and CSS are piece of cake languages and anyone who's working seriously and know the problems of code maintenance know well the pains of not having a good code foundation, a good documentation and a fixed process to make something and not making a big spaghetti code ball.
I've been in projects with CSS files that defined at least 4 layout grids. I'm so happy not dealing that again.