UPDATE: The NYT has an article, dated 5/31/05, on Postsecret. Here's the conclusion:
[I]t is the fakeness, the artifice and the performance that make this confessional worth peeking at. The secret sharers here aren't mindless flashers but practiced strippers. They don't want to get rid of their secrets. They love them. They arrange them. They tend them. They turn them into fetishes. And that's the secret of PostSecret. It isn't really a true confessional after all. It is a piece of collaborative art.