Oh, so many! The sets me and my sister got and building them, exploring the internet and learning English (these are both thanks to Bionicle). Seeing Bionicle sets for the first time at my friends place.
I recall one game where I and my sister would play with the rahkshi. We imagined Makuta as a real dad, and Pouks was the mother who was always angry at him for whatever reason. Vorahk was a rockstar, of course.
The kanoka club! *-* typing in random disk codes, and lots of them would just work (there are only so much combinations with three digits). Reading the Greg reference topic.
There was a time where I was in a Dutch community where everyone had there own little website, and I knew every Bionicle fansite there and I loved building my own. There was the only time I ever rpged.
MOCing was awesome too. I had this flawless custom ussal which would fit in my pocket, so I could always carry an ussal around if I wanted.
Oh, I remember writing an epic! It wasn't bad either, when I look back on it. It was based on a dream I had, and featured three crazy matoran who escaped from a deserted prison and unknowingly got caught in a plot of Krika, and a plot of Bitil at the same time, all framed as a story that Mutran told Vican to convince him to get mutated. Okay, maybe it wasn't perfect. I remember that it started out with a nine-legged creature crawling over the ceiling about to take revenge on its creator. Gawd, I even made MOC's for the story and wrote a theme for it. Too bad I never put them out. I remember the complete theme though, it still like it.
And reading people's Bionicle comics. Man, was I a sucker for that.