Here's what I know:

I'm running Mac OS 10.8.3, with Perl 5.12.4, and I have tried to install CGI::Simple on it. I put considerable time into the effort, and still failed to have it recognized in my scripts. The module works fine on the Linux webserver where my scripts go when ready, but because I cannot use it during development, it has gotten one use, and one only, and that is to assist with the production and download to a client of a zip file from the server. For that feature alone, which gets minimal use, I must enable the "use CGI::Simple" line which is otherwise commented at all times during development.

So, from my corner, I could not vouch for CGI::Simple being compatible with Mac OSX 10.8 with Perl 5.12. It may be that someone else, more persistent than myself, has managed to find a way to get it working.