Not sure if this info helps, but I'm building an online gaming server for a successful and established gaming company, using Scala and Project Darkstar.
Our design is specced to scale to half a million to ten million users (thanks, Amazon EC2!), and Scala gives me extra confidence in my code for five reasons:
1. I catch more things at compile time.
2. It's easy to make much of my game data immutable.
3. Higher level code means that I'm less likely to get a trivial implementation mistake.
4. Shorter, simpler code makes it easier for me to review and find errors. Implicit conversions are a big part of this.
5. The happier I am writing code (and Scala generally makes me happy), the better job I do.
Scala isn't a panacea, and it's got plenty of warts (namely lack of any great tool support) but it's by far the most productive language I could be using for this purpose.
My only complaint is that I wish it could compile down to C or heavily macro'd assembler, as the limitations of the JVM often irk me (type erasure, lack of stack types and by-value object arrays).
I don't think Scala is that popular yet, the 2.8 conversion is woefully behind and has created a rift in the community, and the tool support just isn't there. But if you're a cowboy coder who's not afraid of algebraic type theory and lack of autocomplete, it's hard to go wrong.
If you do decide to use it, do yourself a huge favor and buy Odersky's book. I tried for a while to code in Scala without it, and it was almost impossible to do anything the "scala way" (not that there's consensus on that).
