Interesting thread, though I likewise haven't had time to read all the replies since there's quite a lot already, though I will share my opinion.
Alcoholism in my opinion is an addiction that progresses into medical territory in it's advanced stages. Initially alcohol use starts as something to turn to for comfort or a coping mechanism, whether it be loneliness, bereavement, feeling like a failure, difficult social situations and other things; self-medication. With repeated use, the lower brain learns to associate the situations in which it's used with drinking. The activities, people, times, places and people with which one drinks become 'conditionined triggers', cravings are triggered on exposure (the addiction phase). The learning process is called 'classical conditioning', anyone heard of Ivan Pavlov and his dogs?
Further down the line, as people to continue to drink, they build-up tolerance, need more to get the same effect until eventual they become physically dependent, (it's now a medical problem as well as a psychological one). Further still down, people then fall into a pattern known as 'relief drinking'; drinking to ward off withdrawal symptoms as opposed to feeling good or blocking out negative emotions. In my opinion, alcoholism is not a disease, but a combination of psychological addiction and physiological dependence.