1. The letter of the service being offered
2. The spirit of the service being offered
Personally, I've always thought #2 was more important than #1. Unfortunately, #1 is often the one that gets enforced, especially when lawyers get involved, which is why legalese exists because when you know people argue from the standpoint of #1, you have to make sure there aren't any loopholes. But I'm digressing a bit here...
Look, just because a company offers something "unlimited" doesn't necessarily mean it can't be abused. To argue otherwise is bad faith, IMO. We can argue over where the line is, but that's just a pointless distraction.
But I think everyone would agree that storing a petabyte of data with a service that offers "unlimited" storage for $12/month is abuse.