The ability to use MySQL or SQLite databases, so you can easily store information in your application files without using an external file-based database like mysqli_realted functions are very useful too (especially when working with multiple people from different organisations). I also find it easy enough that anyone - even non developers! could make their own plugin/module if they wanted; though this isn't really something which is needed by most users of Nette's core functionality as there aren’t many third party modules available yet either. It would be great to have some more basic plugins made specifically geared towards storing user data such as login details etc., especially given how simple those things tend to become once we start adding them into our applications. We've been able add custom fields onto forms via nete extensions quite handily but having native support might speed.