in reply to Perl modules and the GPL
... is one triggering GPL obligations simply by "use"ing it?
The GPL only covers redistribution of verbatim or modified versions. If you do not distribute the code, the GPL does not apply.
Now, as far as I understand, this aspect of the GPL has never been really tested in court in any language, nevermind perl.
German courts have upheld the GPL. It doesn't matter though, because if the GPL is invalid, then you're down to standard copyright infringement, and you have no right to redistribute modified or verbatim versions.
The real question is whether the code you write constitutes a "derivative work" of GPLd code. This is where you need good legal advice.