Garrett LeSage committed the unpardonable sin of removing my excuses for not using keys that aren’t on my keyboard but should be. So I choose to painfully remove ignorance from you, as well, as part of my revenge.
My email signature is “Ça en vaut la peine,” which means “It’s worth the trouble;” that first character uses what’s called a cedilla (or cédille, in French). I run across things like this all the time; if I refer to naïveté (which I do fairly often) it’s there twice.
So I mentioned this to Garrett, and he said “Why not just use the compose key?” … to which I responded, quite wisely, “Huh?”
So he showed me a little bit about it, and now I’m using extended characters like ḿáäąâÐ. In fact, I’m having far too much fun with it; it’s very freeing, to be able to specify a proper em-dash without relying on your word processor to get it right.
[aside]I have found myself a complete, willing, dedicated, fanatical convert to Gnome 3. I hated it at first, but now using anything else just frustrates me. I can manage, but it’s no fun. I really wish the Gnome 3 people had a better sense of how to educate people in its use.[/aside]
However, the instructions I found for setting it up weren’t quite accurate for the current Gnome desktop.
Therefore, I’d like to show you — with screenshots! — the way I set up my Fedora 17 installation, such that I use my “menu” key (which sits between the [alt] and [ctrl] keys on my Thinkpad’s keyboard) for character composition now.
First open up Gnome 3′s system settings.

Next, open the keyboard options:

Because this is Gnome, select the “Layout Settings” link at the bottom of the Keyboard page. This takes you to Region and Language:

We’re almost there! Select the “Options” button. (Don’t you like how we’ve selected links, tabs, and buttons so far?)

Lo! We can see our destination now. Open the tree (because we need to add a tree selection to tabs, links, and buttons, you know?) and select how you want to ignite composition. I chose the menu key, so here’s how it looks for me:

Now you can use composed characters to your heart’s wildest desires.
“Linux Compose Key Sequences” is an excellent page that lists compose key sequences, although most of them are pretty easy to learn if not completely obvious.

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I had this set and working in my FC17, but it stopped working for reasons unknown.
With advice from http://www.linuxquestions.org/questions/linux-general-1/compose-key-not-working-4175445217/, I executed ‘setxkbmap -option compose:menu’ at a command line and Writer immediately started recognising Menu as Compose. As advised, I created this command in ~/.xsessionrc
Hope this helps anyone else with the same problem.