There is a way (among many) to find out "some" of the personality and traits, both the strengths and weaknesses of oneself and others, thus the compatibility with others. It can help to understand others and ways to deal with them.

Personally, I find it mostly accurate (if you live long / spend time long enough to understand yourself / others and experiences different / many relationships). In amazon.com, their books rating average is above 4.5 out of 5. 

It is therefore useful to see the accuracy with past and current relationships (including friends, siblings, relatives, enemies, etc) first. For the purpose of this CLM online dating, it might be beneficial (or finding some truth) to know the other person's personality based on their birthday. (or hide yours if you think yours is a psycho, lol)

These are the TWO different websites, for fun or otherwise.

http://birthdaypersonality.tumblr.com/index

http://www.thesecretlanguage.com/check/birthdate/
http://www.thesecretlanguage.com/check/relationship/