Sure someone apart from horoscope sellers has thought of segmenting people according to their zodiac signs before, right? If they can match two people based on their signs, and since each sign has its own assigned objects (stones, amulets), and each self-respecting brand has "brand personality", why not match people to their lucky products then? It seems like a perfect product placement opportunity for enterprizing horoscope writers. Plus, if you know site users' birth dates, does it make sense to show custom sign-appropriate ad units?
In 2001, according to Gallup, 28% of people believed in astrology and 18% weren't sure.