I'm not to sure about your question about proprietry code that relies on GPL stuff. When in doubt, I tend to think "What does Debian do?". They never package proprietry code, so that doesn't help. Red Hat and SUSE do, so that makes me think it's ok.

As an example, just because something compiles under gcc doesn't mean it inherits the gcc (GPL license).

Had you modified LWP in any way, however, you would have had to release your LWP changes as GPL.

I'm not familiar with the Artistic License (PERL), but at work we use a product which stealth installs perl on the hard drive without making a mention of it, and then uses it as a back end. This indicates that either it's ok to abuse the perl distribution license a bit or that the authors of this software are over the line.

You are definately allowed to write your own free version of the software that you wrote for your company, but if it looks too similar you leave youself open to charges of copying. The GNU people do this all the time (it's called Chinese Wall or Black Box coding - you try and reproduce the functionality with no knowledge of the inside workings. Gnutella, ICQ and AIM clients were done like this).

Update Chromatic gives a much better answer below.

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Jeremy
I didn't believe in evil until I dated it.