As long as you're careful to really keep your private keys private; the root of trust gets shifted from a hierarchy of corporations to individuals you know and (personally) trust. I like this "real trust" model a lot more than the current one of a central authority and "being told who to trust", and I think all the advocates of "if you want to use HTTPS you should buy a cert from a CA" are missing this point.
When you hit an SSL site, the remote server (the one you're browsing) presents a number of certificates. One for the actual secure domain, and one or more for the CA that signed that certificate (sometimes more than one because the CA's have intermediate keys. A key which signed a key which signed... etc)
The CA itself is not a party to this exchange, they only provide the end product - a signed certificate.
If you trust the CA (in your browser config), you also trust by extension every certificate that CA has ever signed (barring revocation lists).
