Having been in a school band for quite a few years, I found it essential to tap my foot to keep time. That is what I tap my foot for, to keep the beat and stay in time. It is a reflex now though and I always tap my foot whenever I hear music and I know many people do too like alucard said.
The greatest enemy to what you can know, is what you already know.
It's not how good you play, its how well you play it.