Philip Sturgeon the daddy of Pyrocms and godfather of FuelPHP and Codeigniter wrote a nice introductory article on nettuts regarding Composer (an alternative PHP package manager).

Let’s face it: PHP has had a rocky history with package management, and as a result, it is pretty rare to find a developer who actively uses systems like PEAR. Instead, most developers have chosen their favorite framework, which has code specifically written for it to handle various things, like DB interaction, ORM's, OAuth, Amazon S3 integration, etc.