weird, twice the data, more reliabilty, faster read speeds ... but i guess it takes all kinds
if your one 750gb drive fails, then its also all bye bye, so i dont know where you're going with this
with raid 5 you could lose one drive and restore all the information
the solution is this: 5 250gb in raid 5 = around 1TB
lose one drive, you're good, lose 2 drives at once, its all gone.
i think thats a lot better than putting all your eggs in one basket