Although many broadband providers claim to offer unlimited broadband downloads some in fact do have "fair usage policys" that they can use to implement restrictions on users who they consider to use excessive bandwidth. In most cases the use of P2P (Peer to Peer) file sharing programs is a large factor in excessive bandwidth use as others can transfer files form your computer to theirs and vice versa.

If you are a very high bandwidth user then it is worth checking the full terms of contract when you take up a broadband contract as although some do state they have unlimited broadband in reality that is not sometimes the whole truth.

You may find if you are a very high bandwidth user that your broadband provider may have a few options that they might take. The most drastic being that they could ask you to leave and stop using their service.

Other options that they might implement is to restrict your broadband access. This can be in the form of reducing the speed your broadband runs at at peak times and also possibly if you use P2P File sharing programs restricting these as they are usually high bandwidth tools.

Another possible option you might find is that your contention rate changes and goes up. The contention ratio is a figure that indicates how many other users you could find yourself sharing with at a maximum at any time. Obviously the more users this is then the more resources other users will be taking up and slowing your connection.