Just a quick post to state again: Grid frameworks and responsive websites are not synonymous. For the record, you don't need a responsive grid framework, like Twitter's Bootstrap, to make a site responsive.
It's a misconception I didn't realise existed: Frameworks are handy, but they are not everything. In fact they can be quite limited. Sometimes the old float:left can be a better solution. But this seems anathema to current thinking. And I agree to a certain point, depending on the context.
A responsive site, at its roots, is simply a set of rules to define what happens to HTML elements at certain screen widths: the famous media queries. There is no fundamental need to install a grid framework to make a site responsive, i.e. to maintain some design integrity at smaller screen sizes.
Hacky, but good
Use the same HTML for every screen dimension and squash it into place with some cunning if/buts. Hacky, but good!