1. The stars in a constellation are sometimes thousands of light-years apart and the connection between them is arbitrary.
2. When you were born your obstetrician had more gravitational effect on you than any planet or star in the universe.
3. There are 13 constellations in the Zodiac (not 12). The 13th is Ophiuchus.
4. The Zodiac was established around 2000 years ago. Since then the Zodiac has shifted one sign along, however the traditional dates for each sign haven't changed. i.e. The Zodiac sign that you were born "under" is meant to be the constellation that the sun was in front-of during your birth. So if you are a Gemini, the chances are that Cancer was actually behind the sun during your birth (due to the 2000 year shift in the Zodiac).
5. The natal planet alignment is futile since the time-of-birth is often arbitrarily chosen (i.e. the doctor/nurses may get the hour right, but not necessarily the minutes).
6. Are all horoscopes done before the discovery of the outermost planets incorrect? Planets get found, demoted and promoted all the time. Pluto was identified and became a planet in 1930. It was demoted to "dwarf planet" in 2006. Ceres was a planet in the 1800s and then demoted to asteroid in the 1850s and has now been promoted to dwarf planet again. Xena was discovered in 2003 and became a planet and in 2006 was demoted to dwarf planet. What's more - Pluto doesn't follow the zodiac path like the other planets (i.e. it will sometimes be in front of non-zodiac constellations.
7.If the planets influence us astrologically why is this influence independent of distance? Mars is sometimes the other side of the sun from us and sometimes it is the same side as us, yet this difference has no astrological effect on us.
8. If distances aren't important in astrology, then where's the astrology of galaxies, quasars, nebulae and black-holes?
9. Why do horoscopes of the same zodiac sign in different newspapers differ so much?
10. Why is the moment of birth, rather than conception, crucial for astrology? Why does a thin layer of flesh and blood protect a baby from the planets/stars/sun/moon...a
PS: I think I should say that many of these comments are not originally my own although I do share them with many (thanks to the great Carl Sagan amongst others)