All my storage drives are in my HTPC, I have all my DVDs ripped, TV series, music (smallish FLAC collection) and concert DVDs - nothing superfluous. Some seem to hoard stuff for no reason. Bear in mind HD films come in at 10gb, a HD rip of a tv series can take up 40gb etc.
I have 1x1tb, 2x 750gb, 2x 500gb and 1x320gb = 3.8tb
Though I'm nearly full, I'm doing some encoding now (I currently have a lot of VOB rips and full DVD folders) to save a bit of space on the TV series side, though I like to have my films with all sound sources etc. I'm waiting for the 2tb WD green drives to drop in price. 1tb isnt sufficient a jump for me to warrant, and I like how cool the WDGP drives run (my 1tb is a WDGP).