*Alright then. Im back on track.
I would say that different stages of addiction undermine different functions.
Take a long time amphetamine-addict for one. Why does he take his two fixes each day? Because of a need to feel well (Fe)? I think not, at least not foremost. Long term addictions are often related to Si, I would say. The same function that gives us routine, that tells us to brush our teeth each night or how to peel a potato also makes sure the person with the habit keeps it up. In the case of an addict, it keeps him constantly reminded what his drug feels like and what it tastes like, or the sensation of past times injested. Compare your first ginger-bread on christmas morning when you were little (or whatever) and last saturday, when you sat by your computer and just poured sugar into your system without really even tasting it. Same drug, very different circumstances. You didn't seriously feel well a couple of hours into the second scenario, did you?
Tricky and sneaky as addictions are, they keep us from the truth and ourselves. At first, sure, I would say it's about functions like Ne and Ti. Questioning the establishment and being curious about new things. Then Fe pulls us in when we actually try, granting us chemical joy of some sort. Time goes by and voilá - on to the memory-functions (Si or Ni) as habits. That's really the difference between users and addicts if you ask me (Be it exercise or heroin). Interest or habit?
So I would say Slush is right. To break free from addiction is to reprogram your memory-function. You are still free to observe whilst doing so, but how much are the observations really worth without a healthy observer? Don't break your functions, but develop your less developed ones. Si is meant to make us care for ourselves, you know.
@Duxwing: I tend to use very few emoticons, because I tend to be very clear about sarcasm and ironies myself. They make everything overly obvious for me. In my defense though, I did write three dots, and that's probably as far as I'm willing to go... *Draws revolver from holster and points at Duxwing*