One annoying thing on a fresh Karmic install is the new GDM screen. GDM has been completely rewritten. It is now owned and launched by a gdm user, and it does not provide anymore a real interface to change the settings.
Some are bored by the black background. My point is the user list which displays all names of all registered users. I simply don’t like it.
There are ways to launch the old login settings interface. You can also tweak the gnome configuration with command line if you know what you are doing. To disable the user list at login, you simply have to enter :

sudo -u gdm gconftool-2 --set --type boolean /apps/gdm/simple-greeter/disable_user_list true