I routinely back up my most important directories to an external 3.5" drive which sits on my computer desk next to the gold fish tank. Both hard drives are 500GB and not near full at all. I did get into the habit of storing music on the external only. I have a fairly large collection and find it's a good way to use up extra time. Any type of collecting takes hours of sorting and labeling and the same is true for all those mp3s. Recently, I got very scared when I thought how much time I've spent getting that 52GB of data. I was afraid as I realized that it existed on the external drive only. I needed to have another copy of those audio tracks too.
I saw this little 2.5" Seagate on my computer store's website. It has given me another 320GB in a very small form factor. I rationalized its purchase by thinking I could carry files back and forth to BCIT with it. Of course, actually, I never have more than will fit on a 8GB SD card. Still, even after copying all my music data and every digital and scanned photo I have, I still have 250GB of free space. A man can never have one that's too big though.