Actually, I got my first vest in 2007 and it was so effective that drivers would slow down (and hold up traffic) to look. The trick is the angle, but most importantly the amount of coverage: the more coverage, the better.

My entire vest was competitively covered in the reflective material. The con, is that was not at all breathable, so in the summer I would sweat bullets. I got some modicum of relief by adjusting the zipper.