I used to have the same opinion you did until I started doing some really filesystem intense stuff (not even big, just lots of creating and deleting of files) a

I used to have the same opinion you did until I started doing some really filesystem intense stuff (not even big, just lots of creating and deleting of files) and suddenly my entire system ground to a halt. Huge delays (top showed state "D"—waiting for device). I moved that stuff to its own disk and my system became smooth as butter again. I'm still not down with the traditional unix '"/usr" must be its own partition!' thing, but it does help to separate your tasks onto separate disks.