As a sysadmin, I login to different machines a lot, where I sometimes need to run complex commands that I might need to reuse later (greping different logs at the same time, extracting databases, changing container's max memory, ...). So I had to adapt my workflow to it. I now have a few different ways to make my computer remember things for me:

1. history(1)

I'm lost without it. Seriously. It has saved my ass a lot of times as the default values on centos set it to 1024 single commands. When I need to remember a complex task I do often on a server, I just "history | grep pattern", and then copy/paste/edit. Simple and efficient.

2. scripts

I make heavy use of scripts as remimders, because they're shell independent (if you make them POSIX), and are text files, so you can read them to remember a complex set of commands.
But as they are only available on my local machine, they're not really useful when I'm remotely connected to a server. They do help a lot locally though.

3. text files / wiki

My last resort for procedures and general purpose remind-me-later things. I have a directory on my computer which stores tons of text files about everything I need to remember, sorted by theme:

* certificate.txt to make SSL certificates and export them to different formats
* git2cvs.txt to convert a CVS repository to git
* openvz.txt to setup new openvz containers and configure them correctly
* ...

And many other things. When I need them, I just read them with less and copy/paste/edit the commands.
We also use confluence at work (a wiki engine from Atlassian), so when those notes are well polished and general enough, I add them to the "knowledge database" of the company, for everyone to use.