Time and again I find my harddisk "becoming too small". Adding more and/or bigger disks doesn't really help, they just tend to fill up with all sorts of stuff faster than you can replace them.
Having not enough space left again to download the current Fedora DVD I remembered a little tool I once read about. Maybe it is already widely known about, however for those who haven't heard about it: I suggest you have a look at SequoiaView. It almost like some sort of profiler for applications: while in your code the parts that are really slow are hardly the ones you would expect to be, the things eating up lots of space on your hard drive, too, are seldom the ones you'd suspect.