After some initial frustrations, I got StumpWM working with the new Ubuntu LTS (12.04 Precise Pangolin).
Get StumpWM working with Gnome, so we can use gnome-panel. (I installed "gnome-session-fallback", I'm not sure if this is required...)
This config initially doesn't load correctly, for some reason. StumpWM loads and shows its greeting message, but the prefix key doesn't work and the background is black (or you might still have the background of the login screen). Luckily, after some sort of ~30 seconds timeout, things finish loading correctly and then everything works perfectly.
(I initially thought it was my restarting the X server with Ctrl-Shift-Backspace that made everything (re)load correctly, but that was just coincidence. It turns out that the Ctrl-Shift-Backspace key sequence does nothing while in the initial "limbo", and things just load automatically after the aforementioned timeout.)
In case you really get stuck, try pressing Ctrl-Alt-F1 to switch to a console, then invoke
kill $(pidof gnome-session) (or the equivalent with ` but the wiki is foiling me). This should take you back to the graphical login screen.
Here's what the end result looks like: StumpWM screenshot
[Desktop Entry] Name=GNOME StumpWM Comment=This session logs you into GNOME with StumpWM Exec=gnome-session --session=gnome-stumpwm --debug TryExec=gnome-session Icon= Type=Application X-Ubuntu-Gettext-Domain=gnome-session-3.0
[GNOME Session] Name=GNOME StumpWM RequiredComponents=gnome-panel;gnome-settings-daemon; RequiredProviders=windowmanager; DefaultProvider-windowmanager=stumpwm DefaultProvider-notifications=notify-osd DesktopName=GNOME
[Desktop Entry] Type=Application Name=StumpWM Exec=stumpwm NoDisplay=true # name of loadable control center module # name we put on the WM spec check window X-GNOME-WMName=StumpWM # back compat only X-GnomeWMSettingsLibrary=metacity X-GNOME-Autostart-Phase=WindowManager X-GNOME-Provides=windowmanager X-GNOME-Autostart-Notify=true X-Ubuntu-Gettext-Domain=stumpwm
Assuming you're using the default graphical lightdm login screen (or similar, such as gdm), simply log out, select the new StumpWM config, then login. What should happen is that part of the loading will happen immediately, then you're left in some kind of limbo for about 30 seconds, then things should finish loading completely, automatically. Theoretically.