An interesting thing happened at a meet-up at Square last year. Someone from google's security team came out and demonstrated what google does to notify a user that a page has been compromised or is a known malicious attack site.
During the presentation she was chatting about how people don't really pay attention to the certificate problems a site has, and how they were trying to change that through alerts/notifications.
After which someone asked that if google cared so much about security why didn't they just become a CA and sign certs for everyone. She didn't answer the question, so I'm not sure if that means they don't want to, or they are planning to.
What privacy concerns should we have if someone like goog were to sign the certs? What happens if a CA is compromised?