.zshrc

# Add this to your bashrc or zshrc or whatever

port=`boot2docker info | awk -F=":" -v RS="," '$1~/"DockerPort"/ {print}' | sed 's/\"//g' | sed 's/DockerPort://'`
export DOCKER_HOST="tcp://:${port}"

com.docker.boot2docker.plist

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
  <dict>
    <key>KeepAlive</key>
    <dict>
      <key>SuccessfulExit</key>
      <false/>
    </dict>
    <key>Label</key>
    <string>com.docker.boot2docker</string>
    <key>ProgramArguments</key>
    <array>
        <string>/usr/local/bin/boot2docker up</string>
    </array>
    <key>RunAtLoad</key>
    <true/>
    <key>WorkingDirectory</key>
    <string>/Users/chrisreeves</string>
    <key>StandardErrorPath</key>
    <string>/usr/local/var/log/boot2docker.err.log</string>
    <key>StandardOutPath</key>
    <string>/usr/local/var/log/boot2docker.out.log</string>
  </dict>
</plist>