I wear my work clothes when I commute in. It's about 10 km each way. My work is casual, so I benefit from that (shorts and t-shirt in the summer). Having said that, I'll usually take transit if I have to wear a suit for a client meeting or something like that.
I did commute to a client for roughly 2 months in business casual attire. Really, the key for all cases is just to not go too fast in the morning.