With Scala you get:

1. The performance of Java

2. The brevity of Ruby/Python

3. Static typing with a concise syntax => no need to write tests for type errors. The Lift devs claim allows less total code than an equivalent Ruby app. (See David Pollack on Quora)

4. Functional syntax and Erlang style lightweight message passing, giving you the ability to more quickly pick up Haskell, Ocaml, Erlang etc. if you ever desire.

Not a bad list.

Regarding Clojure, I'm a fan of it too, but wasn't planning on jumping on that bandwagon till the JVM has invokedynamic, lambdas, and closures (eg, Java 8 out and relatively stable). But lots of people obviously are now, especially Rubyists it seems, including Heroku. Why is that?