MySQL via PHP is due to be deprecated in PHP 5.5 (due any month now) so there is intense debate about the future of the database in WordPress. The options are keep safe with through PHP 5.4 until PHP 5.5 and live with MySQL, jump to MySQLi or go to straight up PDO which the PHP documentation insists upon using (which I totally agree with).
WordPress needs to move forward to get shared hosting providers to move on. It’s great. Seriously, WordPress, do it!
Don’t let anyone fool you. Performance isn’t the gain here; it might add a tiny bit. But the true point of this is getting rid of horribly old technologies out of 15% of the Internet. That’s the goal. Or it should be.