Just thought I'd share a little helpful tip. Anyone that has either glassed an airplane, or painted fiberglass parts has run into the dreaded pinhole. For years now at work I've been using a very simple technique for finding them.
Take a bright beam style flashlight and shine it across the surface of your "unsanded" primer at a shallow angle. The light will make the pinholes stick out like a sore thumb. I like to circle them in pencil "very" lightly so I can hit them with a little filler and no more pinhole.
The second photo is a close-up shot of a group of them that shows you how well the light makes them show up. They look massive in the photo, but in reality other than the one to the left they were very tiny. Using this method you can usually kill them all in one shot and not keep finding them as you go.
The flashlight I was using was not the best, but it was good enough for the picture. The one I usually use is WAY brighter.