I always practice and sometimes perform barefoot. I like the traction. It gives me a sense of control. The sustain and soft pedals have lost some of their shine on my concert vertical though.
I prefer shoes, but when I play the piano I usually practice on at home, when I wear shoes my knee often hits the piano under the keyboard. This is uncomfortable, so I usually take the shoes off and play with either my socks or my bare feet, depending on what was inside the shoes. One of the pianos that I sometimes play at church has a very high pedal and I find it hard to control the pedal with my shoe on, so I usually take off my shoe for that piano too. Other pianos I generally leave them on.