WordPress.org

Does it work with mapped domain?

With mapped domains every new domain must be manually created on CloudFlare, as there is no way to do that through API at the moment.

We have asked if adding this feature was something they would consider, and they said : "It's under discussion, but not immediate."

If it will happen, we'll definetly work on it...

Does it sync existing blogs?

No it doesn't, you need the PRO version for that. CloudFlare WPMU Plugin – PRO