Apache and PHP are the same, but different operating systems (or Linux distributions) may come with different php.ini files. I would advise against using short tags ( <?or <?=) if you plan to switch platforms or hosts, as this is a custom parameter.
MySQL is a completely different story. It stores data differently on Windows, OS X, and Linux. Table names are case sensitive on Linux, but not on Windows and OS X. This is actually a bit more complicated. See http://dev.mysql.com/doc/refman/5.0/en/identifier-case-sensitivity.html for all the details.
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