> maybe I'm just old-fashioned but I just have a few folders for paper notes

paper, like.. pieces of paper.. yes, that is old-fashioned! however, in deep math, maybe this is something.. I was told after attending a world-class lecture week in pure math, that it is common for PhDs and post-docs in math to have very little to talk about between each other.. since their interest and subject area is almost certainly deeply buried in some specialty. Aside from the quip "all roads lead to cryptography" perhaps just an excuse for certain people, I can see how this "different worlds" problem in post-doc math might be real..

The fellow writing this post is first-year however.. maybe its different.. Also I just cloned and built pdfgrep .. I am definitely going to try that out immediately .. thx!