Because of all the posts about the pedals I started to look consiously how I do it. I mean, I drive clipless for over 15 years now (yep since the very beginning that they created those things, I felt being clipped the old way was far more scarier), so I tend to forget how I use them.
I almost allways unclip the left foot, very rarely the right. When I hit a crossing with traffic lights I allways look for something to lean against so I do not have to unclip. Here in holland we got the special poles near the traffic light specially made for bikers to signal to the traffic control system that a biker is requested passage and they are at exactly the right hight to lean against.