DBF and I are both right-handed. He puts his left foot down, I put my right down. In my case, it's because I'm more comfortable doing it that way, and has the added benefit of not making me clip out with my left foot. (My left ankle has some range-of-motion issues from breaking it in eighth grade.)

Before I got clipless pedals, though, I'd do BOTH with my right foot. It took a little time for me to break that habit...