is something I did awhile ago, before I really understood how to use SketchUp. Now I'm working on a "dungeon kit" of snap-together pieces that will both allow swift assembly of a basic dungeon, as well as easy adaptation and customisation by the more advanced user. You can move the viewpoint to give the players the sense of 'being there, or it can be a quick-and-dirty way of showing the players .
More along that line, we have the battleboard which I developed, and which can be adapted to any kind of close-in combat; lines of sight are easily established, and character pieces can be moved around the board with ease. This one is designed for D&D and d20 Modern, but I have a GURPS one as well, based on a 1-yard hex.
And finally, SketchUp has many models to use as part of illustrations, either packaged with the program or downloadable from the 3D Warehouse.
I used them to in a that occurred in a game I was running, to illustrate the placements of vehicles.
It's true; a picture really is worth a thousand words.
I will be using SketchUp liberally in any games I run on here.