This is a true story, I have a theory that the time you are born relates to whether you are a morning person or a night owl, I was born at 4.30am and I love that time of the morning, I just bounce out of bed but my sister is the exact opposite she was born 5.30pm and hates getting out of bed!
So to find out what time people are born just have a casual conversation about sleeping or waking up tired or whatever, then mention the theory and they will normally volunteer their birth time or admit that they don't know.
I find it always works!!

Also facebook is helpful for finding out birthdays!