I was on my way to install Net::SSH::Perl when an error with Math::GMP stopped me...
This prompted me to try and install GMP again (though I can't remember now why I wanted to install Net::SSH::Perl in the first place ;)
Following the suggestion here http://gmplib.org/list-archives/gmp-bugs/2006-March/000303.html
./configure --host=none-unknown-none && make && make check make install <<<< GMP installs just fine and dandy. (Well under Tiger on an Intel macBook anyway) And Math::GMP then installs without a hitch or any need to edit Makefile.PL :)
