My butt is always my major concern when I'm riding an upright bike. It usually takes me riding 20 miles/day 5 days/week for 3 weeks to get it to where I actually enjoy continuous day-after-day riding.
I've found Shimano's dual sided pedals give me a sense of safety in traffic situations. There is a platform on one side and SPD clips on the other. I like being able to clip out before an intersection or whatever and still be able to pedal. Sometimes I just stay out until traffic improves.