Most all the current documentation out there encourages PHP developers to use the PDO API. Though I'm still wondering if this is the best option for most developers, as the majority of data driven websites are ran from a MySQL data source.
In most of the arguments I've heard in favor of PDO, they're in comparison to the old MySQL API, which isn't a fair comparison as it almost seems they're intentionally forgetting to mention the newer MySQLi. Both PDO and MySQLi offer an object oriented interface and both support all the most important features like prepared statements and stored procedures. Further, from my understanding MySQLi is better optimized for a MySQL database, offering better performance, an easier to use interface as well as ability to send multiples statements in a single call.
I understand that if you ever want to switch DB systems, PDO simplifies this process. But I don't see why this is such a huge selling point of PDO. Switching DB systems is something that's very rarely done for an application. Further, if you are using proper abstraction of functionality as with MVC architecture, converting to a new DB system doesn't seem to be that major of an overhaul.
If your current system is using MySQL and you don't foresee an immediate need for change, is there any real reason to use PDO over MySQLi?