It makes me laugh what monthly usage allowance some heavy users expect to be provided and the cost that they say this should be.
Whilst NTL have quoted usage allowances they have not said how usage will be measured nor how the user will keep track of his / her usage. Will usage be the actual throughput of the cable modem or the effective throughput where the user will not have the data involved in transmission of headers in the IP layer and lower layers counted against their usage.
Have a look at
http://www.aaisp.net.uk/aa/adsl/adslother.html for a laugh and see what their charges are like. Please note the top up charge for usage above your monthly allowance which is £5.88 per GB.