I've played around with the latest Scala plugin for IntelliJ IDEA and I consider it alpha quality at best. It's hard to get compilation going and it gets often confused with parsing (for very basic files, 10 lines of Scala with annotations for Jersey this time). It feels like Eclipse which will also present errors which are none (for Java!) and after inserting a blank line and saving again, the errors go away.
Scala is harder to parse (type inference, implicits, ...) than Java, but this needs to get better to be usable. They hinted that it's too far behind to get into 8.0, I hope not to far.
But kudos for supporting Groovy, JRuby and Scala and doing their best.
Update: I have the nagging thought in the back of my head and a eerie feeling in my stomach that IDEA can't to better for Scala than for Groovy because of implicits etc. Hope I'm wrong 🙂
Update 2: An update to the Scala plugin destroyed my IDE, it is no longer able to start. It says I should remove the plugin, but doesn't tell me where it is.