You can clone with
HTTPS or Subversion.
I had an EC2 instance which was re-using and old IP. When this happened SSH wouldn't connect as the key in known_hosts had changed. SSHing in to the box manually generated an error, but plow would run with no output at all. Removing the key caused plow to operate normally.
We need to make plow handle SSH errors with an error message that will indicate what's wrong.