It does mention that checks are in place to prevent tampering. "PeerCDN uses a centralized resource authentication server to generate SHA1 hashes of a site's resources. Data provided by peers will only be used if it is safe and unmodified. All peer-to-peer communication is encrypted."

It may prevent tampering, but it does nothing for surveilance. Say hello to passwords.

Surveillance, sure. Like a MITM could be a threat, but a MITM is a threat for any HTTP request.

And shouldn't forms still be posted directly back to the server? If it's just a CDN I don't see how any confidential data could be leaked unless the server serves up your credentials in cleartxt. Perhaps I misunderstood you?