Using Eclipse Helios with the dev-version of the new Scala(2.8) plugin, as there isn't an official release yet. That is beta, definitively -- but I can't confirm the frequently expressed opinion that this plugin is outright horrible ;-)

I'd say, the experience is already OK-ish, and indeed better than the current state of affairs with the Groovy plugin. OTOH, the experience with plain Java is way more smooth (feels like flying at times), and the current CDT I'd rate somewhat in between.

Incremental compile and error highlighting work quite well for me; tweaking a DSL implementation into form just by continuously rewriting your code until the error markers are gone -- without ever having to test-run your program -- is outright fun and just again shows that FP / static typing rocks!

Problems encountered from time to time: - implicits and nested types in other compilation units (esp. nested / super packages) aren't picked up at times when there are still other errors around; they will be picked up after an full build - there seems to be a memory leak in the version I'm using right now (from end august 2010), necessitating to restart the workbench after some hours of work - beware when you're using AspectJ, to make sure you get a version of the Scala plugin which relies on a JDT weaving bundle version which also works with AJDT

PS: I'm using maven builds in all my projects and generated the eclipse projects with the eclipse-maven-plugin, and then imported them as plain-flat eclipse projects. I can just strongly recommend everyone to keep away from the M2-eclipse plugin (for maven) in its current (2010) state, it makes your workbench painfully slow, is buggy and has lots of almost unpredictable behaviour, because it constantly tries to do magic things behind the scenes (and besides that, the aspectj support is broken since this spring)