@JohnLudlow: It's not just mobile code, but just consider the growing landscape of Windows Phone apps, Windows Store apps, desktop apps. Your best bet is to use Portable Class Libraries if you want to share code between all platforms. In any case, stay tuned for a full Pex release with more features!
@aljj: You don't actually need exceptions or asserts. Code Digger will try to create inputs that trigger each branch in your code. If your code can throw exception or contains assertions, then you just get more valuable feedback on how your code might fail.