I say, avoid existing frameworks if you're working for a company. You should be building your own framework that fit your needs without the cruft of pre-existing solutions. This way, you can tailor your solution to your needs and use your own pattern library.
I think CSS frameworks are good for prototyping -- this means, initial product iterations or 36-hour hackathons. Please, please invest in some design and UI development to then build a custom solution when there is a product at hand.
I think the answer, as usual is: it depends. Are you building a prototype for a hackathon, or are you building a product? Hackathon: yes, product: no.