Heh, I wonder how many holes I have in my vision... I tend to be overly retentive about it at my shop, but most of the places I visit only have a couple "safe" seats for execs and everybody else gets to eat beams, which is actually enjoyable for the most part since it's a brief exposure. But I've gotten blammo'd in the eyes before by techs running test patterns and it looks exactly like those flashes in the video that liteglow posted.
My general rule for "safe" is by looking at the corners of a show reflecting off my hand. If the intensity looks brighter than a led penlight then I try to avoid exposure.