>if you start with Android and are NOT certain to cover iOS or WinMobile, in theory it should be possible to build an android app with clearly separated GUI and biz tiers and if needing to switch over reuse the java code in the Xamarin java VM. As the java code is compiled into IL, all [data] structures from java should be accessible to Xamarin forms and other code. From cursory reading almost all things in java 7 covered, but no first hand knowledge. Some glue code expected then, but no need to jump into Xamarin now, unless C# is compelling (and it still IMO is better than java).

I have absolutely no desire to do anything with Java, I'll stick with C# ...