Is AFP (specifically Time Machine) encrypted on the wire? I've been hunting for the answer to this, but I have not found it.  When I back up my laptop using Time Machine to a remote Time Machine server (Time Capsule, or Mac Mini with an external drive), is the data on the network encrypted?

Note that I don't care about the encryption of the data on the hard drives at either end, just about the ethernet/wifi in the middle.
Short answer, no it's not. As with most of the file transfer protocols(SMB, FTP, NFS) it transfers data in plain text.