HBO Attacking BitTorrent
I am allowed to invite my friends into my home to watch my TV, even if they have not subscribed to the channel I am watching -- in fact, even if they do not have a TV licence. And I'm fairly sure I am allowed to lend my home recordings to my friends -- I've certainly never heard of anyone being busted for that, and the practice is almost universal.
Yes, of course you can have friends over to watch your TV, or even let them borrow your tape. What you CANNOT legally do is allow them to make a COPY of your tape and take it home, while you retain your copy. At least, you'd have a hard time defending it as fair use or personal use. Especially if that "friend" is actually a stranger who happens to be connected to the same BT tracker as you. Which is, in essence, what is happening in the case of BitTorrent (and other filesharing networks). A piece at a time, but still copies are being made.
Perhaps these concepts need updating in light of new technologies, but I'd bet dollars to pesos that even if they were, allowing strangers to make digital copies without paying, a la BitTorrent, would STILL not be legal.