There is a (semi) pure Perl solution on CPAN named Filesys::Df. rob_au mentioned it to me the other day and I've been very pleased with it. I have found a bug in it, in that it gets hopelessly confused about the size of an NT drive mounted via NFS on a Solaris box (although it's not enough to worry me). But as far as the local filesystem goes it is spot on.

print@_{sort keys %_},$/if%_=split//,'= & *a?b:e\f/h^h!j+n,o@o;r$s-t%t#u'