I have to agree, it occurred to me the other day that my almost one year old daughter might never have a Windows computer, in the same sense that people 10 years younger than me simply never had an MS-DOS one, except this time Microsoft didn't build the next platform.

Totally dude. Because C# only runs on Windows. You can't use it to build apps for the iPhone, Android, OS X or Linux at all. Nope.

Mono is an option for the current generation to learn one less language. Outside of Windows it's not the default language for anything except Unity3d so curious kids who grow up with tablets might not have much reason to learn it.

So, nobody should learn a language unless it's the "default language" for a platform? What is Python, Ruby or PHP the default language of? Should anybody be learning Perl, Haskell or Objective-C in your opinion?

I'm not saying nobody should but I bet a shitload more people go with natively supported, which might be a better term than default.

And yeah this isn't at all specific to C#. Anything not natively supported suffers - just ask Flash who in a handful of years have gone from a defacto standard to a dinosaur.

I would say the experience is what matters. The user doesn't care what technology the developer used. If you can make gorgeous, fluid and speedy native apps with Mono and C# (which is very much possible) while at the same time making it easier to do cross platform development and deployment then why not.

I recently heard creating mobile apps for iPhone and Android was possible. Forget the library though. I can ask if you're interested to know.