I have a slow laptop and I'm optimizing total boot time. I want to remove the graphical login screen, because I think just typing startx would be faster rather than loading the login screen just to type in my password. I thought the only thing gdm did was the login screen, but running threatens to remove gnome-fast-switcher-applet and ubuntu-desktop!

Is there a way to do this? If I remove the login screen, how can I boot KDE if I ever want to?

Just disable the GDM.

how can I do that?

Try editting /etc/X11/default-display-manager and commenting out the line /usr/bin/gdm. If that fails then additionally you may have to enter /etc/rc2.d (I'm pretty sure Ubuntu loads runlevel 2 by default, you can verify by running 'runlevel' in a console) and move the gdm script (I think it's S13gdm) to a safe place.

I'm almost positive that there's an easier way, but unfortunately I use Kubuntu, and also I don't use GUI tools that often.

System--> Administration--> Services and remove the checkmark from Graphical login manager.

I unchecked 'Grahical Login manager' and my computer instantly exploded.

It went to a black screen that said 'disabling gnome display manager' and stayed there, with no prompt. I logged in on tty1 and typed startx and got my gui back, but it immediately reported that my user-switcher applet has quit unexpectedly, and I wanted to keep it because it allows a guest account. I really like not having a graphical login, but I liked my guest account.

So i went back to the Services menu to turn the graphical login back on, but bizarrely, I cannot unlock the window. Both the window and the 'unlock' button are greyed out! So how can I fix it? I RTFM and found out that I could run it by running . So I tried running and in prompted me for my password, but when the window comes up, it's still greyed out and so is the unlock button!