While waiting for Kubuntu to install itself on the disk, I looked around the desktop and menues. Finding the user sessions I chose one of the other tty's out of curiosity. The desktop disappeared and I got a text console, as I suspected (though a newbie wouldn't).
Reading the text on this screen I found no instructions on how to get back to the graphical interface! _I_ know that I do that by pressing ctrl-alt-F7, but beginners would have no clue and be lost already at this point!
After pressing ctrl-alt-f7 I got a message that the session had been locked and I had to enter a password. I tried using "ubuntu", "kubuntu", "", "live", "live session user", "user", and quite a lot of other passwords, to no avail. I tried searching the internet for what this password might be from another PC. No sensible results. In the end I had to press ctrl-alt-backspace (an option also not available to beginners), change the suggested user name to ubuntu (!) and use the empty password, and start the install over again.
Thanks for the submission. Triaged to Confirmed. I agree, for a new user you can get lost by going through the wrong door. Dialogs can help--as you have suggested. As the Ubuntu user base expands, there will be more poking around with the Live CD and more users getting dropped to a console without knowing what to do. Adding a simple Message of the Day (motd) or Fortune could help users get back to the main menu or reset the graphics server.