Going off a little from the original OP but you asked so...
I'm an etymologist, specialising in names and naming practices.
We tend to consider a name unisex when it hits the 40:60 ratio. There are very few truly unisex names and they of course can change year on year and also, to a certain extent, in different generations. Consider the nickname Chris; in a person aged 40-65ish then it is absolutely unisex. I wouldn't know whether to expect a man or woman if told I was meeting Chris Jones for example. In a younger generation, say a person under the age of 20, I would expect a boy as, statistically Christopher has remained reasonably popular compared to Christine/Christina.
Generally unisex names tend to be shortenings or nicknames (Chris, Sam, Charlie for example) or surname names (Taylor, Morgan, Riley etc...).
And of course names move about as time moves on, there are lots of names that we previously considered male that have moved to unisex and then to female such as Tracy and Kelly. We are currently seeing this happen in the US with the name Riley. It was predominantly male, moved to unisex about 10 years ago and is now a lot more popular for girls than boys (25th in the American charts for girls, 253rd for boys).
Movement the other way, from girls to boys, is a lot more unusual.