If you manage multiple Macs using Apple Remote Desktop and each computer has an administrator account with a consistent password, you can send this script to log into them all at once. Great for Mac computer labs.
osascript <<EOF tell application "System Events" keystroke "username" keystroke tab delay 0.5 keystroke "password" delay 0.5 keystroke return keystroke return end tell EOF
To use this, select the computers in Apple Remote Desktop then go to Manage > Send UNIX Command… and paste in the above commands. This must be run as root. Enjoy!