I'm also bitten by this bug - after an upgrade to Karmic the ~/.xsession script isn't read anymore and my htpc user is auto-logged in straight into GNOME.
Tried to make files in /usr/share/xsessions that launched /etc/gdm/Xsession (or "/etc/gdm/Xsession custom") and also updated my ~/.dmrc to refer to the new session, but it still didn't work and I was logged straight into GNOME (and for some reason ~/.dmrc was reset to the "default" session).
I'm also bitten by this bug - after an upgrade to Karmic the ~/.xsession script isn't read anymore and my htpc user is auto-logged in straight into GNOME.
Tried to make files in /usr/share/ xsessions that launched /etc/gdm/Xsession (or "/etc/gdm/Xsession custom") and also updated my ~/.dmrc to refer to the new session, but it still didn't work and I was logged straight into GNOME (and for some reason ~/.dmrc was reset to the "default" session).
My (admittedly dirty) solution was:
cp ~/.xsession /etc/gdm/Xsession
chmod a+x /etc/gdm/Xsession
Tore