I like bootstrap, but only for bootstrapping my project...or using it for backend/admin styling. Bootstrap is really just a style guide (with some good styles for layout), however if you've got design comps to work from, it's probably better to make your own style guide. I mean, if they could somehow accomplish making this process easier, then that'd be a game changer: basically less like a framework and more like a library.
a good example: If you wanted to rebuild hacker news, would you start with bootstrap? I wouldn't