How about maybe we've reached a point where there are very few things you can't already do/achieve quite well in C#/.Net without having to dip into OSS land?
I'm a C# dev and I keep close tabs on the plethora of tools that become the new cool thing in OSS for other platforms, and maybe it's a case that I don't work on interesting things...but I've never found myself hindered by C#/.Net.
In any case, the major OSS tools out there do have .Net ports that are actively maintained, perhaps only the bleeding edge stuff is slow on the uptake.
I'm a C# dev and I keep close tabs on the plethora of tools that become the new cool thing in OSS for other platforms, and maybe it's a case that I don't work on interesting things...but I've never found myself hindered by C#/.Net.
In any case, the major OSS tools out there do have .Net ports that are actively maintained, perhaps only the bleeding edge stuff is slow on the uptake.