And combining tilly, and btrott:

my $MegLimit=10*1024;
while (my ($User,$HomeDir)=(getpwent)[0,-2])
{
 next if $ignore{$User};
 my $CurrentUsage=(split /\s+/,`du -s -k $HomeDir`)[0];
 next unless $CurrentUsage;
 print "$User uses to much space: $CurrentUsage Kb\n" if ($CurrentUsag
+e>$MegLimit);
};
[download]

Might wanna make sure the user actually HAS a homedir
and that it's not the root dir ;))

Sorry, I HAD to code something... I am SO bored....