I always wondered why you had to develop on a Mac in order to target iOS apps when the target audience for .NET/C# development tools is mainly developers that run VS in Windows.
I wonder how Apple feels about this. I would think that there are plenty of Windows developers that have been considering purchasing a Mac in order to do iOS development, whether it's with Xamarin or through Xcode. If these tools are any good, they pretty much obviate the need to run out and buy Apple hardware (not that this is a large market segment to begin with).
Likewise, this may kill the need for Visual Studio Express 2012 for Windows Phone. If you're a new developer and you're presented with an opportunity to target 3 platforms using the same language that you'd have to learn as you would using VSE, why wouldn't you take that opportunity?