According to Wikipedia, which we all know is true and unbiased...

"Another common myth is that it is illegal to operate a motor vehicle while barefoot. Some people speculate that, because you use your feet while driving, there's more room for error and your feet could slip off of the pedals, resulting in an accident. In fact, in all 50 states and territories in the United States, as well as in Canada, and in the United Kingdom, it is perfectly legal to drive barefoot. However, in some jurisdictions, police officers may ticket you for other things if the fact that you were driving barefoot or in flip flops/high heeled shoes hindered your driving and/or resulted in an accident."

Personally I've never been comfortable driving barefoot, but more than that, the practicality of not having shoes on in case of some sort of an accident or emergency seems foolish to me. My favourite is seeing the rocket scientists riding motorcycles in flip-flops.

I think at the end of the day, it's about having respect for the fact that the machine you are driving in coudn't care less if it kills you, and taking basic precautions when operating anything like that is just logical.