Just a quick post, thought it best here for all of us using google sketch and want some form of easy cfd.
http://labs.autodesk.com/utilities/falcon/
trying it at the moment and as far as i'm aware its completly free. You can do 2d and 3d simulaton. Its quiet good! All you need to do is export from sketchup in .stl (plug in easily found on google)
let me know what you think