It's mostly so I can choose, some will be for me(first tier), some for work(second tier), some for my girlfriend, and some just in case books(sd cards), some reference ones(second tier) and I'll be away from the computer for up to a month sometimes, and will likely be traveling with it in '09, up to a year of travel if I can afford it.
It's nice to have the right book for the occasion
I have a terabyte is called Alexandria, so far it has a library in it and is almost 1/3rd full, so with just 3 cards I will really be picking and choosing.
I collect free books the way some people collect stamps I suppose.