I don't really keep track. I watch a lot of netflix, fiance watches a lot of netflix as well, often we watch 2 different thinfgs. We both also watch lots of hulu plus. I tend to buy too much crap on steam, and I tend to download my steam stuff onto 2 different PCs (gaming PC upstairs, home theater PC downstairs) as sometimes I like to play with the eyefinity setup , sometimes I want to sit in the recliner and play on the big screen.
I would say that on average, I am probably under 100GB, but, I suspect that I have some months where I am 200+ GB