I never really understand the rhyme or reason behind such massive internal drives, I'd be completely paranoid storing anything above a hundred gigs permanently on my mbp - and even a 100gigs is rare for me!
I'd be always concerned of theft mainly (unless also backing up externally, but an internal 1TB PLUS external backup seems like an expensive route!).
I have a 500gb 7200rpm drive in my system and store only apps on it. The rest - all personal files, music and photos etc is stored on a 1TB time capsule and then this is auto backed up to a 2TB Lacie drive - hidden in a very concealed area of my house.
Its just about perfect for me and wasnt expensive at all. My system is totally clean and runs super fast, I can access everything instantly from my time capsule with no noticeable lag, and everything backs up quietly elsewhere out of sight. I cant envisage ever needing more than 3TB total storage.
For travel, if I want my itunes collection or photos with me (not often really) I just tend to compile a few setlists and albums onto my key fob USB. No hassle! If I wanted the whole lot, it would take approx ten minutes or so to dump the entire itunes/iphoto libraries temporarily onto my mbp hard drive and Im away!