Well, back when I was actually attending college full-time, I had a ...certain computer... with combined 4TB of storage space (a nasty web of directory-mapped partitions), and I think about 50GB or so free, but now, since I didn't have a use for that computer, and it's drives all got wiped...but that's another story... I have sworn to myself that I'll never again buy a hard drive smaller than 1TB, and never again will I have that much storage space without RAID5. I haven't started that build yet though, so atm I'm at:
1.5TB external with 58GB free (Rainbow Tables)
1.5TB internal with 403GB free (assorted)
500GB internal with 224GB free (OS/apps/etc) (will shortly be replaced by 2x60GB Vertex's in RAID0, hopefully tomorrow)
EDIT:
As a side note, does anyone have experience using WD EADS drives in RAID5?