We use some modified Bootstrap CSS at Blueprint (ss: http://d.pr/pqCT) for things like horizontal forms. You need to customize it, and new rules sometimes conflict with existing CSS, but it's working pretty well. I've used it in a more primary role on another serious web app and it's great because 2.0 has responsive CSS and has had lots of work done on it to make it stable across platform.
This is a wonderful example of how Bootstrap should work. Everything is familiar but it does not look cookie-cutter. The right amount of same and different go a long way.
