Since I haven't got any desirable answers so far, I am trending into Typesafe Stack. I removed manually-installed scala and sbt and I am using everything from Typesafe Stack. I will update more when I am done testing with this way.
Here is the final update as I promised:
I followed instruction in this link and it worked perfectly: http://typesafe.com/resources/typesafe-stack/downloading-installing.html
Detailed information in case somebody want to follow for Mac OSX:
Basically, I first I switched macport to homebrew following instruction here:
http://bitboxer.de/2010/06/03/moving-from-macports-to-homebrew/
Then I did:
brew install scala sbt maven giter8
Then create a Scala project from command line:
g8 typesafehub/scala-sbt
Finally I followed instruction here to add sbteclipse and convert the project to eclipse:
https://github.com/typesafehub/sbteclipse
Everything works as I expect.