I wouldn't think this would be too good long-term - guys are already prone to things like jock itch in the genital area, which is caused by a fungus that grows in damp places & without breathable fabric, plastic would hold all that sweat & moisture in. I would also imagine this would not be a good thing for females either, since they are prone to vaginal yeast infections. I guess if you're able to do it without having these issues, it might be OK, but I wouldn't recommend it, doesn't seem very hygienic to me...
I too wear plastic pants next to my skin 24/7 with no problems it took some getting used to but after a few months it got easy.