I've had my CapsLock bound to Compose for ages; it's a great use of that piece of keyboard realestate.

I still don't have a good way to discover compose sequences other than by groveling through xkb and compose files. I really wish there were a character-palette tool that would tell me how to type the characters by introspecting the current input settings.

How do you get one of those. Track down an old Sun keyboard? :)

On my last laptop I used the Menu key as Compose. On this one I use Right Alt.

I use CapsLock; lowest usefulness to size ratio possible.

Caps lock is much more useful as a home row ctrl key

Why stop there though? Mine is configured to be ESC when tapped, CTRL when held down. Took a while to get used to, but it's a big improvement compared to other ways of handling ESC on a 60% keyboard.

I find it most useful as a Super key, so that I can attach all my custom keybindings and shortcuts to it.