The Internet Super Hero blog happily notes that the PHP community thinks that "mysqlnd is awesome" and was one of the most desired features to be included in PHP 5.3.

Thanks everybody for your trust in mysqlnd and your support! We shall try not to disappoint you in the future and continue with the development. Of course, as the core feature mature more and more, we will try to spend time on implementing new, useful tricks and try to provide you with additional documentation, if time permits.

They also include a link to a forum entry from Jurgen Krieger who ran some tests via XDebug and determined that connection times dropped, query times dropped and there was less memory consumption overall gaining an average boost of 1000ms from a page.