NTL:Telewest are conducting trials to limit it's cable customers speed automatically to 5Mbps, in effect halving their speed according to Cable Forum.

At the present this only effects the Swansea area, but has also been tested in Preston, but no details have been released as to whether this will be followed by a nationwide rollout.

Heavy users will see the shaping between 4:00pm and midnight, although the cableco haven't given any details on what conditions will trigger the throttling. They claim that 10 percent of it's customers are using 70 percent of their network capacity, although this figure is common for most ISPs.
The throttling, it's claimed, is justified under clause 4.3 of their Terms & Conditions which allows them to "reduce, suspend or terminate your Internet Services." if customers break their Fair Usage Policy.

Traffic management has become a common bone of contention for ADSL users for a long time but it seems cable customers are having the same problems.