One of the things I really like about Folksy.com (the UK-based crafts marketplace) is the cool stuff they make to promote the site. Looking through their Flickr stream, there are plenty of other examples of them getting involved with the community of people who make and sell stuff through the site.
There's lots of inspiration there for us at School of Everything - and for any other startup that's trying to find playful ways to spread the word about a useful service.