Follow up to your edit - and I'm totally familiar with the "Circle of Competence" philosophy, but given Buffett has stated he won't invest in things which he doesn't understand, and he's said he doesn't understand tech, then it's safe to say that he has a "no tech" rule. I've always been unsure of how to interpret the circle of competence thing, as people always develop new skills, so personally I look at it as "only invest in things with which you are most familiar".