"Yes, we're using Scala for some projects at Quora, both big and small. As a programming language, it offers the following advantages: fast, concise, type-safe, object-oriented yet functional, easy parallelism, extensible and built on the JVM. It is also gaining more adoption in the industry and thus getting more support. At Quora, we'll choose the best tools and stack for the product we're building, and that includes our language choices at times."
Here's his blog post about it:
I haven't used it on a serious project yet, but it was pretty easy to work with.