Big thank you Justin for this plugin. It's so powerful and is exactly what I need!
For future releases it would be awesome if there could be possibility to add CSS class to a whole widget block.
Right now there is an option to add classes to widget items ("post_class").
For now I will just add CSS class by registering new widget area in functions.php.
If someone need more info how to do it, take a look into readme.html file in plugins directory.