The constant laughter rubbed me the wrong way at first, but, as the movie went on, I realized that the business men in the film's first half laughed so much because they were miserable. It's an affect, for sure, but an effective one, I thought.
Still, yeah, I can see it being grating. All of Faces straddles the line between genuine emotion and annoying self-parody; even if I thought the experiment was a failure, I'd admire it for going out on a limb.