Although I'd actually been online since around '95 or so, it was around '97 that I started doing Rocky Horror and discovered alt. cult-movies.rocky-horror and another group of weirdos called alt.basement.graveyard...
While I had dealt with BBSes and the like before, the first time I got really into the internet was with MUDs (specifically, LPMuds), which is also when I got really into C as a programming language.
Good times, for a very loose and counter-intuitive definition of "good."