Honestly, in my experience:
- The time you invest in learning the ropes of that framework would be better invested in properly learning CSS. I wouldn't say this of any framework in any language, but CSS is easy and, contrarily to what I constantly hear, it isn't that hard to master.
- Once you know CSS well, it's much faster to convert a PSD by hand than trying to make it work with your framework. The more detailed the actual design, the more this applies.
- The only pseudo-framework that actually boosts styling speed is leveraging a well-maintained css reset stylesheet.
Keep in mind that this is coming from somebody that knows CSS well... I understand why a framework sounds appealing, especially since we have a lot of them on the development side, but in the case of CSS, it is total overkill.