I use Demon and have had no problems whatsoever.
I found this though, fair usage policy is in the pipeline with increasing ADSL speeds

I honestly can't see any ISP letting anyone get away with stupid download amounts monthly in the long run to be honest.
Is the Fair Usage Policy the same as introducing a Usage Cap?
Demon Broadband have always believed that our customers should be able to use the Internet freely and as a result have avoided implementing Usage Caps. This has always been our stated policy and we are keen to maintain this position.
However we are aware that introducing the new high speed ADSL services will enable our customers to increase substantially the amount of data which they can download in a short space of time. Sadly, a small number of our customers are likely to abuse the new services by downloading vast amounts of data at peak times. This behaviour impacts on the rest of our customers by limiting the amount of bandwidth available across the network and means that many customers will experience a degradation of service due to the download behaviour of a handful of users.
As a result we intend to introduce a Fair Usage Policy, to ensure that all our users continue to experience a continued high level of service with their new higher speed Broadband services. This is not the same as a Usage Cap. If a customer exceeds the set limits their service will not be suspended nor will they be charged for their additional usage. However if a customer exceeds the limits of the Fair Usage Policy then their service will run at a reduced speed during peak usage times to allow the rest of our customers unhindered access to the Internet. No extra fees will apply.
Will I be affected by the Fair Usage Policy?
The Fair Usage Policy will only effect very heavy users. Below is a practical guide to how different user types will or won't be affected.
* Customers that use their connection for email and web browsing for at least 8 hours every day of the week would NOT be affected.
* Gamers would NOT be affected - even if they played for several hours every day of the week.
* Customers that download reasonably large amounts of music and video would NOT be affected. For example a thousand music tracks and 5 films every month would not be considered unfair usage.
* Customers that consistently download exceptionally large amounts of data over a rolling 30 day period WILL be affected. For example continually using file sharing applications for the majority of the day over a number of weeks.
What happens if I exceed fair usage?
If you do exceed what is considered to be fair usage over a 30 day period your download speed will be reduced during the period of 9am - 10pm. Your usage will be monitored on a rolling 30 day basis and as soon as usage returns to acceptable levels, restrictions will be removed. At no time will your connection be disabled or additional charges applied.
Full details here:
http://www.demon.net/helpdesk/produc...available.html