What about iOS where you definitely need OSX? Xamarin has some integration with VS (I've never used it myself), but it still needs a mac with OSX installed to work (even if it's just a macmini somewhere.

If Microsoft does buy Xamarin, I'd like the following to happen:

Xamarin and TestCloud become much cheaper. More attention given to the IDE - fix the hell out of it Better documentation

I also think it's a fantastic way of encouraging developers to work on WP 8. The less code you need to port from Objective-C/Java to .net, the better.