Take a stroll in the morning or evening in Hangzhou, and you're likely to spot women wearing pajamas - silk pajamas, usually. I've seen them doing exercises with fans and swords (tai chi?), strolling with friends, and even riding bikes. I remember seeing something on TV one time about the pajama fad in China, and supposedly pajamas are a status symbol; a way to tell the world "I can afford fancy clothes just for sleeping in!"
If you're in a high-rent district, wearing pajamas sends one more message: not only can I afford pajamas, but I can afford to live here.