There is a discussion of this topic
here.
The bottom line seems to be that there is no agreement, but for some people Skype does seem to consume a huge amount of bandwidth. Worryingly, this can happen when Skype is idle and no messages are being sent. It seems that some users act as 'relays' or 'supernodes' and Skype uses their machines to pass on messages and conversations between other parties. You do not get asked if you want to be a supernode or not!