2 500GB's in RAID-0 would be a lot cheaper at this point, but granted it doesn't rallky have the coolness factor of owning a 1TB drive. Just hope these bad boys go down in price when my current 1TB array fills up.
Also answer the question of data security on a RAID system, (A question that pops up ad nauseum) RAID-0 = potentially less secure... (If one drive fails all data = screwed) RAID-1 = twice as secure as a standalone drive (both drives would have to fail simulatenously in order to lose your data, however 2-500GB drives would only show up as 1 500GB drive). RAID-5, which I've never personally used yet seems ideal, you would have 3 drives, faster access, and more security (I believe two or more drives would have to fail simulatensouly as well to lose data, and 3 500GB drives would show up as 1 - 1TB drive)