Hard to say, really. I know after I first flew in the game, it was an experience that sealed my love for the game. Of course, I took breaks here and there, but I always came back. I suppose, for me, it was after I got into using Mids' to make my characters silly powerful. I stopped taking breaks after that, and made a whole slew of themed alts with builds that tried to pull off different things.
Of course, the friends that stuck around to the end also helped make the game more than just a sometimes distraction.
I think that raised things to a whole new level - getting the ability to fly, and earning the right to wear a cape while doing so. Flight and combat flying in my opinion made super speed, leaping and teleporting unnecessary. (Of course though, team teleporting to mission target was mighty convenient..)
