I've seen never seen anyone barefoot in a regular weightlifting type gym. But there's an area of the gym I go to where mostly women do calisthenics on pully type machines in a class setting and they're usually barefoot. My wife does pilates at the same gym and will only remove her sneakers and socks when she's on her own mat for the class and puts them back on before leaving, but when she goes to a yoga studio to do her regular yoga she leaves the house in flip flops. She said the gym just seems too dirty and public compared to her tiny yoga studio. I will say the yoga studio is a nice opportunity to appreciate nice feet and for the few times I've gone there, I've seen some "interesting" stuff once or twice.