I fiddled about with it briefly a while a while back and it seemed decent enough, both upload and download speeds were fast and consistent. The Windows client app was rather unintuitive at first and also a bit of a memory hog IIRC, but not really a problem on a modern PC, and no showstopping bugs that I can remember.
The main aspect putting me off was having to log in every 90 days or else your files will be deleted - I know it's probably not an issue in practice, but I just don't like having these niggling concerns in the back of my head. And of course your "free" storage is tied to your status as a BT customer, so if you change provider you'll have to make other arrangements.
Personally I wouldn't use it as my primary cloud service, but if you're entitled to it and can make use of it in addition to the other options out there, then why not.
