Running the 20101126 snapshot, I was poking around a bit this morning and noticed a possible permissions issue.
$ ls -l /tmp/ssh-U7b26QotNu5v/agent.12708 srwxr-xr-x 1 test wheel 0 Nov 28 15:57 /tmp/ssh-U7b26QotNu5v/agent.12708 ssh-agent (1): $TMPDIR/ssh-XXXXXXXXXX/agent.<ppid> UNIX-domain sockets used to contain the connection to the authentication agent. These sockets should only be readable by the owner. The sockets should get automatically removed when the agent exits. [...] A UNIX-domain socket is created and the name of this socket is stored in the SSH_AUTH_SOCK environment variable. The socket is made accessible only to the current user. This method is easily abused by root or another instance of the same user. Should auth-agent be setting the socket permission to 0700?