As stated, the official rule is that the mugs are good for one resort for one stay. Most resorts have signs posted that state so... However, in practice WDW has a "Free soft drinks for guests" program at the resorts. Old mugs, mugs from different resort, non-WDW drink containers are used by guests will little or no ill effect. CM's don't care in large part, and those that may say something are probably new on the job. When asked, most food court CM's will say they are good for life, even though a sign over their shoulders contradicts them. Other CMs will tell you that as long as the mug has "Disney" somewhere on it, it's OK. Basically, chaos reigns. People, like me, that stick to the "rules" used to champion them here, but quite frankly I've decided that if WDW doesn't care enough to lift a finger to enforce their own rules (other than responding to e-mailed queries with the official policy), then why should I waste my energy? I think that's why it's gotten calmer here on the topic.