I'm not sure...I've had both incredibly accurate and incredibly inaccurate information pop up. I think how much the results of a reading affect you boils down to how much importance you give it, how seriously you take it.
Once I heard, "You MUST go to the doctor right away. Something serious is wrong with you." (And nothing was.) And as far as enneagrams, life paths, etc...I've found ones OTHER THAN MINE that describe me and what I'm about, far more closely. I'm not very Taurus-like in comparison to a couple of other signs.
And at a new age expo, some lady told me that my "birth animal" is a beaver. I was like...."uh....beaver? I bet you say that to all the girls..." She explained what a beaver was (which was 100% opposite of me). I told her that she had just described my polar opposite. She justified this by saying that I'm out of balance, and sometimes people who are out of balance display the opposite characters as their animals. (Malarchy, I thought...my balance has always been more related to my bra size than anything.... And I thought it was pretty darned rude for some lady who didn't even know anything about me other than my birthday to make the presumption that I'm out of balance.)
Then again, I've had a couple of tarot readings (always depending on the deck...the Angel Deck is awesome, the Crowley Thoth deck has been pretty doomy), horoscopes, etc. that were dead on. My Meyers-Briggs profile is dead on.
My mom asked if I'd like a psychic reading for my birthday in a few weeks and I told her a gift certificate to Jo-Ann Fabrics, or paying the ransom to remove the pop-up ads on my writing website, would give me just as much gratification.