I've been watching discussions like this for a while, and I just have to ask:
How much "stuff" do you need to keep forever?!! How many movies have you seen that you're really going to want to watch again?
I have about half of my 5TB filled, and mb adds it up to 75 hours. I have a very few movies that I've moved to a "watched" folder that I may consider rewatching some day, but most get deleted and, eventually, replaced. Which is one of the many things I love about an HTPC.
Granted, we don't have kids, so I don't need tons of Disney stuff (though, I admit, I have a bunch).
With what are you folks filling up 12TB???