A runner posted a comment in the forum at about.com about running clothing. I replied to his comment, and I thought I'd post my reply here for those who don't read the about.com forum.
Many years ago there was a runner named Dr. George Sheehan. He was one of the legends in running. In one of his books, he talked about running clothing. He said you could tell the newbies, because they had the latest fashion. The experienced runners wore grubbies. Running shoes, of course, were an exception to his statement.
Things are different today, because running clothes have improved, and wearing the latest clothing has advantages to runners in extreme conditions. I bought my first poly T-shirt last summer, and I'll never go back to cotton. I bought my first 100% poly socks last year, and I'll never go back to cotton. I do, though, wear mostly grubbies. I'm still wearing my nylon running pants that I bought 25 years ago, and I still have my nylon wind breaker that I bought almost 30 years ago. When I layer for winter, I include old cotton shirts that still fit but are too worn to be used as an outside layer. Cotton is a good insulator if it is kept dry. If it gets wet, it is dangerous because it freezes.
You're right that training counts! And, I would add that common sense about pushing yourself too much or too little in training counts, too.