I do write down stuff, and I kept a dream diary for a few years, but I don't worry about remembering ideas. If you forget them, were they really important? Ideas are cheap, there will be others.

Certain obsessions, things that I'd rather not publish, stay in my mind until I forget whether I wrote anything down.

In general, notes in text files on the computer are easier to find back than notes on paper. But I still have to do something with OneNote on my pc in order to import the articles I wrote in OneNote on my phone on the plane back from Lissabon.