I've tried this several times, but I always find that by the time I've been stumped by something enough times to write it down, I'm on the verge of having it learned anyway. So, my cheat sheets just become random bits of paper full of stuff I already know, and I start new ones. Rinse and repeat. It's a nifty trick but I don't think there's any substitute for good ol' repetition and understanding.
http://www.mediaatelier.com/CheatSheet/
Hold 'command' key to see all shortcuts for current application.
I have a git repo with work notes in.
It all goes in there:
root@osboxes:/space/git/work/notes# ls | head
7z
abs-guide
algorithms
anacron
angularjs
ansible
ant
apache2
apt_and_dpkg
Not quite the same, but similar: Print-to-PDF. I've been doing this instead of bookmarks for years now, and as a result have a huge library of local PDF's, usable offline, for all kinds of technologies that I'm interested in/use regularly. With a few key searches I can find all the docs on luarocks, or mysql FAQ's, etc. - I find this a great way to have searchable local documentation for the moments I need to look things up. Its not quite a cheat sheet, but having my own local searchable PDF archive for all the technical howto/tutorial-style HN articles of interest over the years has been invaluable.
I keep appending to a file in my home directory. I've aliased it too so that I can access it quickly. Every ~month I email it to myself or back it up elsewhere.
$ alias ed
alias ed='$EDITOR ~/.diary"
The file looks something like this:
# 4/3/2015
Command Comments
-------------------------------------------
M-l # Emacs, lowercase next word
Hm. How about a cheat-web-link? This stuff's gotta already be online, neatly summarized.
My vim cheatsheet lives in my dotfiles repo. Always gets cloned into a fresh system.
If you like this idea, you might want to check out Cheatography - it's a tool for creating stylish cheat sheets. I used it a little when it was first announced, but haven't kept up with it. It's a great idea, and the developer was really friendly when I was checking it out.
http://www.cheatography.com/