To re-phrase Parkinson's Law:- "Data expands so as to fill the space available for it".
As an ordinary home user I would shun such capacity on one HD, with so many eggs in one basket. If I needed anything like that capacity I would buy a number of external HDs instead and partition none of them.
I echo Diemmess' Eggs and Baskets not for the likes of us strictly commercial, and then with caution
I have 1O hard drives excluding the system. 2 are in caddies a 200 Gb and a 10Gb back- up and 7 in the rack[ all salvaged small drives but OK for putting in a caddy to back stuff up on- in addition to burning to CD/DVD - In this lark you cannot have to many belts with your braces
TB hard disks will become the norm and to say they should be shunned because home users won't know what to do with it is, well, funny!
I can't wait to get my hands on TB disks to fill up with all the video, music and photos I have busting out of my measely 2 x 160gb disks.
As for management well most folk will buy a new PC with Vista on it and high end machines will contain TB disks... Vista file management and search facilities are meant to be the best. So I don't think users will get lost in between platters.
I'm not a Luddite, but I am talking of now. I agree that your second HD may be too small for your needs.
I just think it is premature to consider having a primary HD with a capacity far greater than needed (for reasons 1-3 in my last post), because of the time and difficulty in backing up its contents against the day Drive C: fails.