There is no such thing as unlimited. Hard drives have a hard limit. And bandwidth costs hosts a pretty penny. So they limit what you can not do to use too bandwidth. What hosts don't advertise is the limitation placed on inodes and mysql connections.
Their TOS states that while your using all this unlimited resources, you are prohibited from lots of bandwidth hogging activities and if you hog more than a certain percentage of CPU and RAM resources on the server for more than a set amount of time, you get the boot for TOS violation.
They offer unlimited because in reality, most sites will use a bare minimum. Those who seriously take them up on the offer, get the boot. But what do you expect for $5 - $10 a month?
What cracks me up is the Professional Web Host who offers unlimited storage for $18 a month on the VPS when the company that owns and rents out the VPS offers their top tier VPS for $170 a month with a 160GB disk space limitation, and also has a 1500GB transfer limit. To make matters worse, there is no TOS to abide by.
Maybe I'll rent it for a couple of months for that $18, fill up the entire disk quota, and stream video all day and night until the monthly transfer has been exhausted, and let him foot the other $152.
CoffeeCup... Yeah, they are the best!