Considering the Weaker Brother?

Aside from Luther's famous tract, On the Freedom of a Christian, almost every article I read on Christian freedom is written as a warning against exercising one’s Christian freedom at the expense of the weaker brother. This bothers me for a couple of reasons. First of all, I do not think sufficient time is given to defining the identity of the weaker brother. Second, few ever take a minute to understand the original issue Paul addresses and if such issues could bring another person into perdition and cause them to lose their faith. Has anyone ever lost their faith because a Christian showed up at a high school dance? Has anyone lost their faith because they saw a pastor smoking, or drinking a glass of wine? And if so, what exactly was their faith in?