I finally figured out the keyboard shortcut for em dash (and en dash) in Gnome. I don’t have to type the lame — any more, I can be a real man and type the right thing — . If you don’t know what an em dash is, you better read about it on Wikipedia.

Se here is what you do (this worked on my Ubuntu Hardy Heron Linux system):

Go to: System > Preferences > Keyboard > Layouts > Layout Options > Compose key position

and check ‘Right Alt is Compose’.

Et voila!

Now whenever you need to type an em dash, just hold the Right Alt and type three hyphens.

— = Right Alt + —

Similarly you can get an en dash by holding Right Alt and typing two hyphens and then a period (you can leave the RIght Alt before typing the period).

– = Right Alt + –.