Me,
I need more space.
Although i dont specifically have a single terabyte drive. i have a 1000gb(just shy of 1tb) raid setup and a 320gb drive. at the moment i have around 250+gb free in total.
I have the 320gb drive for all my isos, 30gb from the raid set aside for vista. 15gb from the 320gb drive for osx, just under 300gb of dvds waiting to be xvid-ified, around 300gb of xvid-ified dvd rips(subs, multiple audio streams ie commentary etc).
about 50gb of digital photos from around 5 years or so.
about 25gb of mp3 music 192kbps. which i just trimmed down from around 45gb.
and a bunch of stuff ive snatched from computers at lans, work, friends etc.
but yeah i dont really think the average user would need the space.. but digital video is a major user. im only dealing with dvds and its taking up almost 300gbs.
imagine once you start dealing with hi def dv streams of almost uncompressed footage..
all i can say is that if they can make it why not..eventually the price will come down and it will be a no brainer to get your 750/1tb drives.