This is just a pre-announcement to let folks (OSes, hosting providers, other platforms) plan and do integration work. Per our own warnings, we definitely don't want this running on production machines until it launches in 2015.
Our Apache code is a developer preview, we'll be working on Nginx next.
ISRG will be operating a new root CA for this project. Although if you think that your choice of CA makes you more or less secure, you may not have understood how PKIX works -- you can buy a cert from whichever CA you like, but your adversary can always pick the weakest one to try to impersonate you.