I really like this. I could have used it at the last 2 places I've been at. The only annoying thing is that it does not handle directories out of the range of the size of a CD.
I know it's easier to say "hey your thingy doesn't do this really neato thing" rather than stating the same, and then giving a solution. Alas I am far from providing solutions, but I though you'd like to know this is a nice little program.

UPDATE:
Oh for heavens sake... Had I taken the time to look a little more closely, I'd have seen that changing du -sk to du -dk gives a MUCH more granular look at the directory tree below where you invoke the script.
Good stuff!