Rob points out, with regards to the problem with Zend Studio apparently ignoring your php.ini file when using the "internal" debugger, that Zend Studio comes with it’s own pre-compiled versions of PHP, which it uses when debugging.
So, if your php.ini file isn’t in /usr/local/lib (and mine isn’t, it’s in /usr/local/php4/lib, as a result of a dual PHP4/PHP5 setup), then the internal debugger won’t see your php.ini file at all; and that’s why it seems to ignore your settings.