Okay, I'm gonna continue talking about drinking for a second, and I agree with Nicklar that this could be its own thread.
Japan has a social drinking culture. If you get involved with Japanese people, making Japanese friends, and going to Japanese events, you will likely be drinking. It's the same kind of mentality as visiting an old buddy was 30 years ago in the states. You show up, they offer you a beer, you drink. Within the ALT communities, if you happen to have one nearby, you might find people who are not part of the Japanese social structure who are okay with non-drinking events. Also among younger Japanese you will find many non-drinkers as well, but after a certain point this becomes much harder. Being the non-drinker at an event that isn't ALT run can be amazingly stressful from my own experience, and the only reason I wasn't drinking is I had had a bit too much the night before.
However, all of that is related to Japanese people and Japanese drinking culture. ALT drinking culture can be highly varied from non-drinkers, to nightly drinkers, to full blown alcoholics. A lot of ALTs in their first year tend to go a little overboard at the beginning as well, which is understandable given it's a new experience, a stressful experience, and for many it's the first time they've been this much on their own before in their lives. Finally, there is the problem that in many cases it's a very different type of alcohol to consume and some ALTs have to find their limits again... Me and Japanese beer do not get along... it goes down too easy (mainly because its tasteless... like coors light) and before you know it you're three sheets to the wind with the worst preservative headache you've ever had coming the next day

All this means is you could spend a lot of money, being outside the group really can suck, and drinking culture is very different in Japan.