I used Scala on a project a year or so ago. I needed/wanted to target the JVM. However, after looking at Java the language, I realized how far it was behind C# now. (I hadn't used Java in several years after going to work for a Microsoft shop).
Scala was fairly easy to learn, the new features of C# really coalesced nicely with the Scala language, so I didn't feel like I had to learn much.
There are some nice features of Scala (var/val immutability, etc) that would be nice to see in C#.
I think Scala adoption in the .NET community may be hampered by 1) continual improvements in the c# language and 2) the F# language.
The F# language in particular because it has full IDE support.
The Achilles heel of Scala was lack of really good IDE support. Coming from C#/Visual Studio, working with Netbeans and the Scala plugin was somewhat frustrating...it wasn't quite ready for prime time. (Considering it was the work of one person, it worked very well but had a few issues).