I just ran the tutorial successfully. My server is 'valkyrie' running ubuntu 10.4 and my client, 'wraith' is OS X 10.6.1. Make sure you use your client rsa/dsa key and not your server's. Here's my example:
echo "ssh-rsa AAAAB3NzaC1yc2EAAAABIw...== mwilliamson@wraith" | sudo -H -u git gitosis-init