The difference is that I can basically count on any arbitrary java/jvm program running on Linux, but even with Mono I don't get that same level of confidence with random c#/clr.

Now this may be largely a culture thing, with Java programmers creating more cross-platform software and avoiding platform dependent libs just by default, or it may be a technology thing, but to the end user it doesn't really matter.

Sure, you can run command line c# apps just fine but the web hosting solutions for c# web apps are terrible compared to IIS + Windows.

And this is coming from a linux veteran who wrote a C# web app and hosted it in production on Linux for a few months and then had to re-write it in .NET MVC hosted on IIS. I hate Windows servers. Every time I have to RDP into them to change some configs instead of just vi'ing files in /etc I want to shoot myself.

I love the Mono project, and I follow its progress with great hope. But I've tried to use Mono apps on my Mac (Popcorn Hour configuration things) and they flat out wouldn't run. The gui came up and it just hit a brick wall. I tried it on my Linux laptop... it showed a bit more... and then got stuck. I ran upstairs to a windows machine. Finally it worked. So the write once, run anywhere mantra hasn't exactly hit all Mono developers yet. I think C# is one of the best languages I've ever been blessed to use, but Mono still has a ways to go.

Yes. Mono is not C#, it’s only a subset.