right now I have 5 hdd's on mine for a total of 1,650 gigabytes. That is way more than what most people need I use 500 gigs strictly for storage space. 250 Gigs is used to to run XP and a bunch of games I put on for the grand kids. The other 900 gigs is used for various periphial stuff. I have all kinds of junk on it for saving radio/TV broadcasts etc, I have a lot of wireless stuff set up so I can net work with mydaughters PC.
I don't get out much so the PC is pretty much my window on the world. I also have a lot of books saved on it, Which are Mostly audio and visual Qur'ans, Hadeeth, Arabic Language courses, So although the HDD space seems too high, I will probably have to add a few more drives. I only have enough space left for 3 more internal drives, but have plenty of room for external ones. I do have 3 external USB HDD drives, One is just a total back up of my operating system and major programs.