Man, i haven't seen Sketchup since about version 3 and i'm glad i followed my inclination to download it today.
My intention was to display models of famous landmarks to be able to get a rendering to sketch of them, and boy i am totally amazed.
What an awesome artist tool, with in minutes i had downloaded the Sydney Opera House and was able to display shadows all set by the Sun angle at different times of the year, even though i have 3Ds Max experience there was absolutely nothing to it, it takes just minutes to download a park scene complete with tables and benches and roman Colosseum, or perhaps a skyscraper, or even a person in 3d form, there are literally thousands of models to choose from.
Being able to change the time of day and time of the year gives you an unlimited set of variations of highly accurate shadows "Real Shadow Details" produced instantly, with very very simple controls, i'm in sketching heaven, i'd had enough of photo's and i have now found my new sketching resource.
Either type in your browser Google Sketchup version 7 plus you will need the latest Google Earth, version 5, and bob's your aunty
The links: Sketchup comes in both the Pro version and the "Free version" the Free Version is what i was using
I've put a snap of my current view