I remember having a gentleman over I think to fix something or other and when he walked into the living room he explained my crt monitor was misconfigured and to his perception had a visible flicker. We checked it and it was indeed misconfigured although I couldn't see it but it was such an aberration to him that he took time away from his actual job to make the flicker go away.

You will also note many items in the post above are papercuts that might go unnoted like input feeling a little worse or font issues.