Do you hate having a bookmarked PDF or notepad with all of your app cheatsheets? I used to have a Google Docs spreadsheet that was just full of them, but it became increasingly difficult to sift through and find what I was looking for. By that point, I might as well have not used the shortcuts at all.
That is why I love that I found Cheatsheet, an app that actually handles all of those shortcuts for you. It runs in the background, and any time you want to check the cheatsheet for any app you are using, you bring up a page of the shortcuts. That's it...super easy to use, and full of useful key combinations you didn't even know existed.