Interesting... NetBeans is multiplatform, lightweight and fully supports code refactoring.
As a matter of personal taste, I'd rather choose eclipse+PDT or an eclipse-based IDE like Aptana (free) or Zend Studio (not free).
I also write JavaScript code and for eclipse there's Spket plugin that offers the best support for editing Javascript files, especially if you're using frameworks like jQuery/Dojo/Ext.
A minor glitch I don't like about eclipse - though, is their implementation of "go to next/previous word" (when you press Ctrl+Right or Ctrl+Left)... Works well for CamelCase coding-style (used in Java/Javascript/PHP-Yii) but doesn't fit well to FuelPHP coding style ($lower_case_underscore)...
Which IDE you're using usually depends on your own personal taste, corporate-policy and/or what else are you using the IDE for.
Would be interesting nonetheless to see what people are saying here... as FuelPHP is a young framework and uses namespaces...