BT's cloud?
Shame there's no mention of how the product works and if it's in any way related to the original Bittorent protocol.
Article: "The premium version it's announced – US$39.99 a month – claims unlimited-size file storage" yet according to wiki there is no cloud, only your devices:
"The user's data is stored on the user's local device instead of in a 'cloud', therefore requiring at least two user devices, or "nodes," to be online in order to synchronize files between them", and
"There is no limit on the amount of data that can be synced, other than the available free space on each device"
Either something has changed and they're now another cloud storage provider or they're charging you for storage on your own devices.
My guess is the former.
http://en.wikipedia.org/wiki/BitTorrent_Sync