This was sorted out back in the dial-up days when providers (including the one I worked for) offered "unlimited" dial-up service. Customers sometimes argued th

This was sorted out back in the dial-up days when providers (including the one I worked for) offered "unlimited" dial-up service. Customers sometimes argued that they should be able to stay connected 24/7 all month long because that's "unlimited". Our definition (that we indicated in our terms) was "you will never be billed a surcharge for usage during a month", but there was no guarantee of being able to use a certain number of hours. So we reserved the right to de-prioritize (i.e. disconnect) high-usage users during peak times to allow other users to get on when our lines got full. I'm sure somewhere in Crash Plan's terms of service they define what the term "unlimited" means in the context of their offering, and I would bet it means "there will never be a surcharge for usage of storage". So they will never ding you for using more than X storage, but there's no guarantee that you can store a specific amount of data on the service.