>>>John also makes a good point about Xamarin being overkill if you're only going to be targeting one platform, Android. However, my argument for using Xamarin is that the code and the development environment will be something familiar, C# and Visual Studio. And what happens if you don't use Xamarin and then they want the app for iOS too?

>>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# ...

was meant as a technical answer to the now embolded part (and sent to Pete directly as well).
I often said I think C# to be superior to Java, but as it is more accepted among my typical customers over here and the default for Android as well, there are points balancing the language "feel".

As in the OP context was no mention of a hybrid desktop/mobile app, the reasons NOT to choose Java are somewhat diminished, and porting from an android first is possible without entering the whole Xamarin tool chain just for the option to later branch out to iOS