Wonderful stuff. :) I only have one gripe and that's with the following:

if ($DEBUG) { print STDERR "Debug: some value"; }
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is pretty clear, but if we re-write that one line, it becomes more of 
+a conversation with the maintainer:

print STDERR "Debug: some value" if $DEBUG;
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I do agree that the second line reads like English ... but it doesn't scale well. Consider this:

if ($DEBUG) {
    print STDERR "Debug: some value";
    # some tempory line to debug our debuger ...
    # some other temp line ...
}
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The difference is to never use one line for such if statements because sooner or later you are going to want to put another line in the block. Even if it's just temporary, you are going to have to rewrite the second line so you might as well accept that all if blocks will always take up at least 3 lines. I have adopted this practice for about a year now and it has served me very very well. YMMV naturally. Great mediation man! :)

L-LL-L--L-LL-L--L-LL-L--
-R--R-RR-R--R-RR-R--R-RR
B--B--B--B--B--B--B--B--
H---H---H---H---H---H---
(the triplet paradiddle with high-hat)