The Architectural Illustration ‘Digital Watercolor’ Technique by Scott Baumberger is beautifully presented on Ronen Bekerman's blog. The slide players show the steps taken to bring the sketchup linework through a suite of colouring and effects in photoshop to create the final images.
I like this idea of taking the 3D model data through to a looser creative image environment. This is similar to the work of a colourist working on comic pencils/inks. Plus using multiple passes from Sketchup is sensible as well.
[Arch Viz image by Scott Baumberger via ronenbekerman.com]