I recommend perlbrew over relying on macports' perl. Many other ports rely on it's version of perl, so using a cpan tool with that version can mess things up, just as with the system version. Also, do you have example of which CPAN modules fails on OSX. I've never had any problems with the many XS modules I've installed and developed, except for EV, which was just the author being refusing to workaround a compiler bug.