For my lossless FLAC music server and 1200+ CD collection I need about 400 GB of online storage (300 MB per CD) plus OS space. I have 650 GB since I actually use more than one OS install for development, plus I'm still buying CDs.
> Do you really listen to all 10GB of MP3s - delete what you haven't listened to in a year
I buy my music, and quite often will go a year without listening to one specific CD, but it's sweet to have it playable in 10 seconds just by scrolling to the right folder when I am finally in the mood to hear it.
For my desktop box I could get by with perhaps a couple of 80 GB, but have a 120 + 160 since they only cost a little more.