How can I get Onboard (the screen keyboard) to stop launching every time I log in?

Looks like this bug is back in precise (tried using update manager, didn't work) This is the only solution I found:

Open a terminal window and type the following commands:

cd /etc/xdg/autostart
sudo rm onboard-autostart.desktop

It was a bug: launchpad

You can use Update Manager for fix

Let's try two things here. Open the Terminal application and type these commands:

gsettings set org.gnome.desktop.a11y.applications screen-keyboard-enabled false
gsettings set apps.onboard xembed-onboard false

The first command toggles whether the screen keyboard should be visible, just to make sure it is supposed to be turned off. That is the same as the option under System Settings / Universal Access.

The second command makes sure OnBoard does not show when you unlock the screen. This is the same as opening OnBoard Preferences and finding that checkbox. Sometimes that option gets enabled and it doesn't change back.