I'm male RL, and 99% of the time I play a female avatar. In 13 years of playing in SL, I've only been challenged maybe 2 or 3 times. I've even participated in voice chat using voice morphing. I think gender swapping happens way more than people think or admit to, and if you think you can always detect it, well you only know for sure about the ones you actually get suspicious about and catch. You can have no idea how many you don't detect.