"One big text file" was a big deal a while back. Here's a post by Merlin Mann:

http://www.43folders.com/2005/08/17/life-inside-one-big-text...

For notes, I keep trying all kinds of apps and approaches, but I always come back to a single big text file. It's surprisingly easy to search. The main thing is it's just so convenient.

Edit: This is a better link https://danlucraft.com/blog/2008/04/plain-text-organizer/