I've been using index cards for syntax issues and to remember some commands. It's a tremendous help.
If I forget a somewhat common but not heavily used command that means I need to get out of programming mode, flip to a browser, Google it, find it, then either paste or write out the command.
Knowing it off the top of your head means you're done in 2 seconds without any context switching.
I can't remember the number of times I had to google on how to convert the human readable permissions in linux to the octal form but I had to use it a lot in my chef adventures.
Code:
stat -c %a <file or directory>
I have that just sitting on an index card and I don't think I'm going to forget it for a while because I looked at it like 8 times.