I've tried to optimize things so that while working, I can get things jotted down with close to zero resistance. If the barrier of entry is too high then I don't bother doing it.
That means often being able to spawn a new terminal, write a command and be done with it. Or to be able to pipe something from my clipboard into an auto-dated file.
I ended up putting together this ~15 line Bash script which seems to do the trick: https://github.com/nickjj/notes
I've been using plain text notes since 2001, although I only recently created this script. So far so good.