It's great to see the HN community responding positively to news about .NET/Mono and related tech. I've been working with C#/.NET since 2008 and always felt it's a vastly superior platform to Java in every way. It's a shame it is taking so long for the wider tech community to realise this.
I've spent the two halves of my career thus far working on each stack, and I really can't see where those sorts of claims come from, honestly. C# as a language is a win over Java, but from an operational perspective, it's a disaster--IIS is an absolute nightmare. Beyond that, I tend to think that because of the niceties that C# has over Java, that has somewhat held back .NET community adoption of some better practice…
Java don't have async/await, but .NET already has it for years. Lambda expressions for Java were also released many years after C#. I prefer properties in .NET comparing to getter/setter functions in Java. There are other advantages of C#, just check tread about this on stackoverflow.