For me its dependent on whether one has a good view of the opposite gender or not while will make it akward or not depending on the situation. I've run into and made situations like that a few times on older RP boards that I ran. So imo I find it as a role that extends oneself and not just a character. If a guy can RP a girl well, well, that just means that the guy is very fimilar with the female throught process and vice versa for girls RP'ing guys. Although you do find more girls rp'ing guys better then guys rp'ing girls.