Hi Nightrain,
That's a good question! Personally, I believe that it's a common thing to experience both male and female lives, although I do believe some souls have a preference and feel more comfortable as one specific gender. All of the lives I remember are female - I am perfectly happy with that (real girlie girl here)!
Most of my friends who remember pl's have at least one recollection of being the opposite gender. During a meditation, my mom once saw us together as two young boys - brothers. Although I have no recollection of it, I don't doubt I've had at least one flip of the coin.
Aili