There is no such thing as true unlimited hosting. You really need to look closely at the terms of service. Unlimited accounts are subject to a backup limit. Once you get to a certain number of files, or reach a disk space limit your backups stop. This is typical of unlimited hosting plans.
At GreenHostCo, we are taking the honest approach. We offer green hosting with no hidden limitations. The disk space and bandwidth limits are clearly stated for each green hosting package.