Thanks for the insight. When you mean "grab my lovely grid", do you mean just view the grid in Fireworks to see how many pixels apart everything is and code to match it? If so, I'm pretty suprised the mockups are "pixel perfect". Seems like mockups are a lot of work. That's done twice.
No - at my agency the design team works to a 12 column grid which makes responsive design a bunch easier, by "my grid" I mean our pre-built HTML/CSS in house framework for working with this Grid style. It's loosely based on Eddie Machado's Bones framework [1] but integrates well with Magento too.
[1] http://themble.com/bones/
