Systems like the WikiWikiWeb "replace technical security with social and political limits" (CliffordAdams). The WebOfTrust concept attempts to create technical security that is based on the social strength of the community.
The [epinions] community uses a combination of a web of trust and a web of distrust.
How it works, using PrettyGoodPrivacy (PGP) as an example:
The PGP cryptography system allows you to sign another user's key, indicating that you know the user and have verified with them (in person or over the phone, usually) that your copy of the key matches theirs. Once you've signed a key, this means that you can trust communication encrypted with that key.
Here's the neat part: Not only can you trust that key, but you should also be able to trust other keys which that key's owner has signed. And keys which those keys have signed... and so on. Thus "trust" flows from individual to individual. You have confidence in people you trust, and also in people whom they trust, etcetera.
The system also lets you weight your trust. For example, you may have complete trust in one key's validity and its owners ability to sign other keys, but only partial trust in another key and owner. This partial trust also reflects on other keys verified by that key.
The exact mechanics are described here: http://www.rubin.ch/pgp/weboftrust.en.html
(See the TrustMetric page for discussion of what "trust" means.)
A good (fairly long) paper on webs of trust is Khare and Rifkin's Weaving a Web of Trust:
Check out an idea for WebOfTrustModeration.
For example, there is a program on the site that lets an Apache server restrict access to web pages to people in your trust neighborhood.