CaCert is a Certification Authority that works with a web of trust: people meet and assure (similar to keysigning) eachother. If you’ve been assured by enough people you’ll be able to let your ssl server key be certified by cacert. It’s a lot more secure than other CA’s who just give anyone a certificate who pays enough.
Still a hierarchical system with a CA is flawed. When the CA is compromised, the whole system fails. PGP’s web of trust hasn’t got this weakness.
(Got a nice shiny cacert certified ssl certificate on my webserver now)