While I generally use Scala for my personal projects I'm a .NET/C# dev by trade. There are definitely features about the .NET ecosystem that I wish I had on other platforms and that they worked as well as they do on .NET. I'm thinking about features like LINQ (sorry, Squeryl is nowhere near that yet) and the top-to-bottom integration of VS.
I'd like to see more attention paid to it as well.
As a certain lawsuit is illustrating, C#/.NET is much less coupled to MS than Java is to Oracle. Oracle is suing Google for creating an implementation of Java without their blessing, a clear indication that they believe they own and control the platform. By contrast, Microsoft has issued a legally-binding pledge not to sue people for creating their own implementations, and published the platform's spec as an open standard.
Mono admittedly lags a bit behind Microsoft's implementation of the platform, but that's mostly a question of resources. If Mono had been embraced by the open source community the way Java has been (as it should - see previous paragraph), then that wouldn't quite be the case.
Though not by much, and not in all respects. That crew is doing some really great stuff.
I've been saying this for a while now that I'm starting to sound like a doomsday-sign-carrying lunatic. C# is really enjoyable to code in, but it's a shame that it's stuck on Windows.
I'd like to see more attention paid to it as well.