Twig & Drupal: state of art I'm a really newbie in Drupal world.
I use Plone since 2004 but now I've to learn also Drupal for various reasons. 
I'm reading books and tutorials, using this CMS as power user and many more.

Now it's time to go deep and the first thing goal is: theming from scratch.
I've notice that PhpTemplate it's not exactly a clean pagetemplate system (for my point of view), while Twig seems very interesting, but I don't understand if Twig could be clearly used in Drupal7 or not.
Twig is in Drupal 8 core, but you can use it in Drupal 7.
Check out this sandbox that provides twig as a theme engine.