Pbacot: see http://en.wikipedia.org/wiki/Microsoft_Visio
The "professional" version includes dozens of architectural smartshapes.
Before Microsoft bought Viaio from Shapeware, they were making a concerted effort to compete with AutoCad, even buying intellicad as a transitional strategy: see
http://en.wikipedia.org/wiki/IntelliCAD

But when they sold to Microsoft that effort was deemphasized.

Nick Sonder: Re designing from the start in 3D: sometimes I do that if the site terrain is a major factor (as with your ski houses) but most of my work in on flat sites and except for a few exterior steps, terrain does not play a factor in designing the floor plan. I'm a big believer that the focus of CAD should be Design, not Drafting. And the failure of most CAD software is that it's mainly aimed at drafting not design. And I believe that in early preliminary design for most projects (not if you are designing Bilbao Museum) 2D manipulation of accurately dimensioned spaces (as opposed to physical building objects) is important. As I said before: I never ever have to draw anything by hand. And therfore everything I do in Visio flows directly into Sketchup.

I agree Nick: If I didn't have Visio I'd be doing exactly what you are doing. The advantages of Visio in preliminary (2D) site and plan design, where Sketchup is weak, (and Acad is terrible) are too great to ignore. This discussion is about CDs I know, but I'm usually producing design floor plans and 3D models for 3 schemes on any project before starting CDs.
Once I'm doing CD's the single 3D model for the selected scheme is the basis for coordination: The only disadvantage I face when I change the model: I have to export and import jpegs for each view affected whereas you just do an update from within Layout. It's a tradeoff I think is better in my situation.

I stumbled upon the 6 Sonder videos, then this forum, which inspired me to share my experiences. It's great to see what you folks are doing, but overall I'm not ready to jump to Layout for anything. See below for why it's not yet worth it to me.

Background: I'm a sole proprietor (like Nick Sonder) doing houses, additions and renovations. No employees. I do all my own drawings including structural and electrical.
(see millikenarchitecture.com for examples of 3D and 2D DESIGN drawings.) I never use a pencil. (except on site to record existing conditions for a reno.)

Mid 90's I adopted Shapeware's Visio (in beta and long before Microsoft bought it) for 2D. I found it much better than AutoCad especially for plan design and also for CDs.

Then I jumped on @last.com's Sketchup in Beta in 2000 and adopted it for 3D. At the time Sketchup was called ("Visio on steroids"). Long before Layout existed I evolved a workflow for construction documents very similar to Sonder's but using Visio instead of Layout for 2D.
(exporting jpegs from Sketchup and importing to Visio for elevations and sections, and section cuts for section drawings to Visio, then adding dimensions, masks, grade lines, notations etc.) The Layout approach involves less redundancy because the 3D model is referenced dynamically but unfortunately the section cuts cannot be.

I looked at Layout at each release to replace Visio but believe it has a long way to catch up for both preliminary design AND construction drawings. The main problem with Layout is that scrapbook objects are dumb. I'm no fan of parametrics for most physical objects, but for notational objects, Layout is limited to standard dimensions. Visio has dozens of indispensable smart notational objects and an easy way of making your own. For instance:

Preliminary Site Design: Zoning limits are always crucial for my work. I start with the survey which I can input using smart boundary dimensions (bearing, arc length and angle, and closing bearing); then add zoning setbacks (smart offset dimension lines straight and curved, dimension drop from point perpendicular to property line); and smart area labels for overall site area and footprints of existing and proposed structures and decks. I can insert a live referenced and properly formatted excel object to show allowable coverage calculations.

Preliminary Floor plans: Visio is excellent for 2D design iteration and layout of SPACES. At this stage I want to manipulate 2D spaces (rooms) not walls. Visio has smart room labels showing overall room dimensions like real estate plans like to show and clients can read. When I'm ready, Visio has dynamic self joining wall objects and an overall grid environment that makes 2D design and iteration very quick. I can poche walls to correspond to various types (new, existing, demolished). It also has multiple object alignment tools, equal spacing tools and polygon Boolean tools still missing from Layout. (Nothing ever has to be "exploded" to proceed further so smarts are never lost.)

3D Design: Once I develop a few preliminary plan schemes in 2D: then I export to Sketchup to begin the process you all use.

Construction Drawings: When my client chooses a design scheme, then I start CDs as I described at the top. Again Visio's smart shapes beat Layout hands down.

Of course Visio has a somewhat different interaction environment than Sketchup, but then again so does Layout.

Eventually I hope Trimble integrates the entire Sketchup/Layout system into one program with two modes: 2D and 3D. Then if they enable smart scrapbook objects, I'm ready to switch.

If you want examples of my CDs in PDF I can upload.