HA - pitfalls include needlessly using low level functionality when any number of hundreds of higher level (to varying degrees) frameworks and libraries that would abstract away most of these problems, and easily installed/found with composer/packagist. Why most PHP'ers ever need to write a mysql(i)_* function is beyond me. There are plenty of perfectly good wheels out there and you're not re-inventing a better on.
That's assuming that the users have the server access to install the packages or an up-to-date PHP interpreter. A lot of the appeal of PHP is that it is available on cheap shared hosting, which until recently would not be guaranteed to have PDO, mysqli and friends installed. If you have access to a VPS of some sort, you can easily install such things, but in that case you can also use a different language.
