Window -> Model Info -> Statistics -> 'Entire Model' from the pulldown.
You're looking for 'faces' number. It will be close to the polygon count, not quite the same; because sketchup uses n-gons. The actual polygon (quad, 4 side poly) count will be little higher. I think 10% to 15%, from what I've seen so far.
Though in some cases, it could actually be lower, through some simplification of the mesh; deleting unneccisary polys, and what not.

Friends don't let friends use booleans.