I ride in full cycling-specific gear -- cycling shorts and tights, jersey, jacket or vest, shoes, helmet, etc. My commute is 30 miles round trip on hilly roads. I ride year-round and cycling gear keeps we warm in cold months and cooler in hot weather. It is so hot in NC for much of the year that I almost always get sweaty, even in winter. My cycling gear will dry out during the day at work, so it is dry for my ride home. If I wore street clothes, I'd be walking around in wet, sweaty, stinky clothes most of the time at work. I also would be much less comfortable riding.

Like others, we have showers at work. I carry work clothes in the seatbag on my bike or on days when I drive. I also leave certain items at work(eg, towels, shoes, spare pants, extra clothes). If you can ride to work in street clothes and arrive at work dry and unsmelly, more power to you. Not possible with my commute.