Same here -- started reading fic in the late 90s but have no recollection of Character/You fic being a trend. I hail from X-Files fandom, though, where I think people had such strong ship preferences (or of course the NOROMOs had a strong no!shipping preference) that they didn't do much self-insert fic? Even so-called Mary Sue stories weren't much of a phenomenon (misogynist trope conception aside).