In Ubuntu Hardy 8.04 and also 8.04.1, when you set up your compose key and you activate the automatic login, the compose key is not set at all everytime you start you computer.
I found a quick and clean fix for this using ~/.gnomerc.
Here’s how :
At first, you can just try and run this command:
setxkbmap -option compose:menu
Actually, this will set up the Menu key as the compose key. But you can change this how you want.
Open or create ~/.gnomerc (you don’t need root privileges), and copy and paste this text:
#!/bin/bash export GTK_IM_MODULE=xim setxkbmap -option compose:menu
Change the chmod to set it executable:
chmod +x ~/.gnomerc
Just reboot to see the changes. It seems to work everytime, at least better than the gnome-control fix I used to use.