More Than Pretty
We have a slightly different perception of what designers are at 37signals. It is not so much about making things pretty as it is about figuring out what things should be and how they should work. That requires looking at the things themselves and not at the frame, or other elements that will fall into place naturally later. Once you have a really good message design, creating the rest in some ways is trivial.
I like this quote from a recent interview with David Heinemeier Hansson (creator of Ruby on Rails). A good designer gets to the essence of a thing, emphasizes it, and minimizes the rest.