I've been fighting against learning SketchUp for quite some time. I always thought it was too simple. Wasn't organised. That not much was possible with it. That it didn't have the features which would justify its place amongst "real" modelling packages. However, a few quick under-pressure stints using it at work and at home have changed my mind. Completely.
It's not by any means a "full" modelling package, of course. Its not really right for organic (anthropomorphic) or hardbody modelling (automobiles, etc) - no sub-d's - but what it does in terms of accelerating basic box modelling is fantastic. It allows extremely accurate and easy box modelling in minutes. What takes minutes in Softimage takes seconds in SketchUp.
If you are doing Archviz, use it. Once you get your head around it. You won't look back. You can quite easily design a building from scratch in SketchUp, possibly to a level of detail which you could generate drawings from (using the section tool).
My workflow is now:-
1. Flesh out the main building in SketchUp (use export with instances) - the "Sketch" bit.
2. Import into Softimage. Clean up mesh/de-triangulate/etc. Add more of the fine detail, scenery. Unwrap. Add materials/textures. Add Lights.
The free version exports the Collada format which can be brought into Softimage more or less intact using Crosswalk.
I found this out pretty late in the day (due to the new Valve Steam update bugging out all the SDK apps) but there is also a plugin by Valve for exporting vmf and smd files. It's in the SDK directory. While I probably won't use it, it does mean that fleshing out levels is much faster than using Hammer. Hammer is SLOOOOW and needs a rewrite.
And this my main bane with most 3d packages... Sometimes 3d just takes so bloody long... (rant over)