This has been floating around for a few years now. Companies offering unlimited bandwidth and unlimited hard drive space. The answer to this question is an obvious no. There is no such as unlimited bandwidth and unlimited hard drives, therefore it's just a tactic that many hosts use which is called overselling. The majority of users never use their allocated bandwidth or space assigned, and many hosts take this into perspective when managing the plans they are offering to end users. You will find that some users can and will use all the space assigned, for example anyone using an image hosting service or file hosting service can take advantage of the unlimited bandwidth and space feature and basically kill the server. Well, not in actuality, most hosts also counter this by having a CPU clause or resource clause which would state if your site is using a certain % of the resources that your account can either be suspended or terminated.
Unmetered vs Unlimited:
There is a difference. Unlimited means there is virtually no limit, which is frankly impossible. Unmetered means that you will not be billed for any extra bandwidth being transferred but you still technically have a limit depending on the type of port connection you are on. You'll see some hosts advertising 10MBit port and 100MBit port. The difference being, if your server is maxing out the 10MBit port, it is still technically unmetered but your server WILL come to a crawl, until you find a way to drop the amount of traffic being transferred OR upgrade to a burstable connection, which you'll have to pay more for.