Comment 1 for bug 369988

This is because an entry is set in the session manager. To stop it starting at login, open the "Startup Applications" gui from the System->Preference menu. Scroll down and you should see an entry for gnome-do. Make sure it is un-ticked. If this report is a bug, I would say that it is because the gnome-do application has its own option to start at login which is clearly not honored in the default install.