The biggest problem with C# is the .Net ecosystem. Without (much) an open source community, it is and remains a tiny pond, full of crap, including a million shitty web applications and all the .Net baggage (Visual Basic anyone?)
There's a ton of open source code out there, from Mono, Gnome, a lot of projects on Codeplex, and a bunch of other sources. I don't know where the myth that there's a lack of open source .NET code came from; it's simply not true.
Thats true, but it isn't so much the baggage, as it is that you can't distribute a program written in C# unless your users have the .Net runtime installed, which is a pretty fucking big download.
It is 2010, and it still doesn't have a linker (this wouldn't have mattered so much if the programs where still distributed on a CD, but it sucks when you have to download that much).
Which is a damned shame.
It is a beautiful and fun language.