Why belong to an association?

I'm always on the lookout for research or articles in the mainstream media that extol the benefits of association membership and volunteering. Here's one such article that appeared in WaPo yesterday. If you ever find a similar article or research, please send the link along.

Go-Getters Use Groups to Get Ahead: "Because by participating in professional organizations -- including alumni organizations, organizations that target professionals from your field and your demographic, advocacy groups and training organizations -- you may gain credentials and contacts that are just as important to your career as those yielded by your paid experience, many professionals say."