Are there any events being fired on the Windows Phone 7 (Mango) when you:
a) stay in a view for so long that the screen goes to sleep, and you unlock your phone and return to the app?
b) tap the windows button and then the back-button to resume the app?
Yes when you stay on a page long enough the OnNavigatedTo event for that particular page is fired.
When you resume an app the Aplication_Activated event on the page App.xaml.cs is fired as well as the OnNavigatedTo event of the page is fired.