I guess I could sing "Not an addict" like
K's Choice used to. But I'm a tv show addict. I don't watch that much tv but the series I follow, I can't bear to miss one episode!
I can't wait for the new season of
BSG,
Lost,
Dr Who...and I sooo want to see
Ashes to ashes ! I guess that I will follow
Torchwood despite its flaws and weaknesses, if only for Gwen and Owen.
Nip/Tuck is the only show I'm not that eager to see again, I think it jumped the proverbial shark at the end of season 3 but I know me I will probably watch the 5th season nonetheless! And I will watch
Grey's Anatomy too even though its soapish side often bothers me.
There are shows I'm not addicted to. I never followed
Alias for instance, I saw a few episodes though. Sometimes I catch and watch
Desperate Housewives or
Bones on French tv but I don't follow them either. And I am not feverishly catching up with
Rescue Me. Those shows aren't necessarily bad, some of them are quite decent, but I'm not hooked. Most of the time I've only seen a few episodes and missed many episodes inbetween so I never became an addict.
So apart from a very good writing and intriguing plots and endearing characters, I think it's all about the serial side of tv shows. Cliffhangers aren't what makes you keep going. Provided that the whole thing doesn't completely suck, once you're on the train, and after several successive episodes it's difficult to give up. You just go with the flow, and of course the more you do the more you're hooked. Maybe that's the reason so many Buffy viewers that obviously despised the late seasons kept watching the show while cursing Joss' choices.
As soon as you're an addict you may become a fan and do crazy things such as posting on a fan forum or discussing your favourite show on LJ. It's the next step but it doesn't necessarily happen. I'm obviously addicted to several shows, some of them I did love, but
BTVS and possibly
BSG are the only ones that turned me into a fanatic. If you've become a fan it's doubtful that you could ever be cured of your addiction for you will keep feeding it even after the show has ended on screen. You will watch your show on DVD, you will go on mentioning it on the Internet years after its end, you will use quotes from episodes at several occasions and gather with people from the same fandom. And of course you will read fanfiction.
One last thing. I believe that the Internet increases the possibility of becoming an addict, and of course a fan. It's so easy to get tv shows online these days. It's even easier to follow a series than on tv because you can just go by your personal RL schedule and catch up afterwards, or make up for a possible unavailablity.