whenever i get a new game, i tend to be briefly obsessed with it for a little while. for instance, i got pokemon ranger (guardian signs) and pokemon mystery dungeon (explorers of the sky) for christmas, and so far my playtime between the two games is almost at 60 hours. pokemon games in general tend to get me pretty hooked, though never for longer than about two months. my previous heart gold file had about 700 hours before i reset it. in fact, that's another thing that i like to do. sometimes if i don't have any new games to play, i'll simply go back and restart a file on any one of my numerous pokemon games, then clear the main story in a few days and continue to play afterwards. i think that's one of the best parts of the pokemon games; you can play a single pokemon game multiple times, and get a different experience each time based on what pokemon you raise, etc. ... pokemon games in general are very addictive imo. at least for me, i can play the same one for months and months.
it also goes without saying that pokemon online (and a few months ago, shoddy battle) is extremely addicting. it's so fucking hard to just stop yourself from clicking the find battle one more time. when you win, you think "o i'm on a roll!!!!". when you lose, you think "fuck ok well now i have to play even more to make up for lost points!!!!!". it's like a never-ending cycle of addiction -.-
unlike some people, i'm not too irc-addicted. in fact, i don't go on irc all that often, as i tend to frequent smogon during the day in numerous small, 10-15 minute spurts, which really isn't enough time for me to hop on irc and chat (or at least i don't think it is, though i'm sure that some users would disagree). irc is fun and really time-consuming/addicting once i allow myself to get into it, but usually i don't even bother to log on so i rarely have addiction-ish problems with it.
one last thing: fuck super smash bros brawl. i've forfeited thousands of hours of my life to that fucking game ;_;