I've been using C# for over a year, and I think it's a great language.
<< C# is a language developed for the .Net framework which executes in a Runtime environment similar to Java's Virtual Machine (sorta). This means it is going to be about as slow as java, but it may be a little faster because it is tailored for windows >>
Actually, it should be quite a bit faster than Java as it is JIT compiled.
I think the real question is, will you learn .NET? I think if you're a developer, you're doing yourself a serious disservice by not learning .NET, especially if you're a windows developer.