I've done just that, sans .NET of course (through Mono). Developers must keep current no matter who makes paradigm shifts in languages. And I'm happy to say that I've quickly picked up C# since it's so close to both C++ (my proggie of choice) and Java. Now I guess I'll start tinkering with C++ .NET.
I'm still working thru more C#.
My hobby is making games, and I'm trying to build a middle-tier for an online wargame I've got. I'm going to build it in both Java and C#.
I am hoping that the C# might be faster. The Java is fine for a turn-based game, but it's too slow for an RTS.