I often run across sites that I think may fit the Soul of the Web. PostSecret.com was one of them that I had thought about but never got around to adding.

From Wikipedia:

PostSecret is an ongoing community art project in which people mail their secrets anonymously on one side of a homemade postcard.

Here is a CNN article from Jan 2007:
The secrets people reveal

Unfortunately, as of today, the site seems to be gone.

And the rumors are running rampant as to why:

PostSecret Site Shut Down Over National Security
Post Secret considered spam blog, mistakenly shut down?
Is PostSecret Dead?

In the meantime, here is a recent video on YouTube about Post Secret: