I've been using IntelliJ IDEA for Scala for about a year. Best IDE ever.
With Scala IDE I've only had painful experiences, plus I hate Eclipse with a passion - but folks keep telling me that it got better. Well, I don't really care as long as IntelliJ IDEA exists.
They are also extremely fast and responsive in fixing bugs of any kind. I personally couldn't be happier and other communities can only dream about such IDE support. Of course, if you compare IDEA's Java support with the Scala plugin, it's worse, but IDEA works better for Scala than Eclipse does for Java, like seriously ;-)