Sky who operate a mixture of an unbundled network and the BT Wholesale IPstream service where they have not put their own hardware into exchanges has rejigged the way usage allowances work on their products.
The Sky Max product uses ADSL2+ via Sky LLU kit to offer connection speeds up to 16Mbps and was previously subject to a fair use policy. This has now been removed which means we can expect to see marketing describing the product as unlimited in the near future. For an extra £10 a month on top of an existing Sky TV bundle this represents good value. Most other truly unlimited products are significantly more expensive, though how long the product will remain with no fair use policy depends a lot on how many people are attracted to the product who try to download 1000GB or more a month. People buying the Sky Max product should not expect performance approaching 1:1 contention levels, as this is simply not possible for £10 a month. If there are a handful of heavy users on an exchange people may see little or no congestion, but over time as the product becomes more popular this is likely to change.
The Sky Connect product which is what you can order for £17 a month if your exchange is not unbundled by Sky is due to have traffic management of some type applied in addition to the 40GB monthly allowance.
While no fair use policy applies, Sky has retained a section in the terms and conditions that all providers have in one form or another, and that is that they reserve the right to protect their network and maintain quality of service for all our users. Generally this is interpreted as a clause allowing them to act if you are found to be using their mail servers as spam relays or similar malicious behaviour, but it could apply to people that for example saturate their downstream capacity every hour of the day for months on end.