Would never dream of using BT again. As other users have confirmed, your speed will be throttled back to 0.5Mb/s if you use your connection heavily or for p2p apps, even if you are paying the full ?35 for the unlimited option. Huge charges for line transfer and early cancellation make the value for money non-existant. I payed the full amount to the end of the contract when cancelling early, then got charged and extra ?70 on top for early cancellation - It would have been cheaper to let the contract run out.
Customer service is shockingly bad, technician to move the line never turned up I set-up everything myself. Stay well away.