Bear Pajamas & Kigurumi

A few weeks ago, I wrote about the bear pajamas that Lain often wears in Serial Experiments Lain, wondering if it was perhaps a cultural thing or maybe an Anime convention. Several people commented, and commentor Lily posted an interesting explanation yesterday:
These pajamas are indeed a cultural thing in Japan. It's a part of Japanese street fashion and the costumes are called kigurumi. People wearing them are called kigurumin. There are a few firms in Japan that produce these costumes, the most popular one of them is Sleeper's.
Interesting. Lily also links to a page from their site which has a bunch of examples (no bears, though). A brief check of Wikipedia yields some more info:
Kigurumi (着ぐるみ?) is the Japanese name for costumed animal characters. The name comes from the Japanese term (着る - kiru: to wear) and (縫いぐるみ - nuigurumi: a stuffed toy animal).
To wear a stuffed toy animal. Heh.