I use SketchUp for schematic design of my projects. I used to use Form Z but gave that up because no one else uses it anymore. Anyway, here are my two most recent projects, one an architecture school, the other... a psychiatric hospital. Yup.
I definitely have to upgrade to 7.1. The school model there on the bottom is about 58 MB (is fully modeled on the interior too), and the hospital with site file is about the same (doesn't have an interior yet).
I'll be using SketchUp to model some ideas for our new house. We're planning on re-doing the kitchen, and we can possibly test some paint colors. I have to actually get in the house though and measure it first.