I was just reading in SilverStripe Core Development Google group that the internal developers use PhpStorm for development. I was wondering that if anybody from the core team sees this post, if they could share their setup/settings. It'd be really cool if we can get some silverstripe code completion!
I also like using PHPStorm. It's a great IDE for SilverStripe development.
Some SilverStripe-specific things like the $db variables do not auto-complete. But that isn't too big an issue for me. Otherwise, like swaiba says, it all just works out of the box. Version control integration is great, too.