June 2012: Android 4.1.

• You must explicitly request the Android.Manifest.Permission.ReadCallLog and/or Android.Manifest.Permission.WriteCallLog permissions; access to the call log is no longer implicitly provided through Android.Manifest.Permission.ReadContacts and Android.Manifest.Permission.WriteContacts.
• Android.Widget.RemoteViews will throw an exception if setting an onClick handler for views being generated by a Android.Widget.RemoteViewsService for a collection container; previously this just resulted in a warning log message.
• New Android.App.ActionBar policy for embedded tabs: embedded tabs are now always stacked in the action bar when in portrait mode, regardless of the size of the screen.
• Android.Webkit.WebSettings.AllowFileAccessFromFileURLs and Android.Webkit.WebSettings.AllowUniversalAccessFromFileURLs default to false.
• Calls to Android.Content.PM.PackageManager.SetComponentEnabledSetting(Android.Content.ComponentName, Android.Content.PM.ComponentEnabledState, Android.Content.PM.ComponentEnabledState) will now throw an IllegalArgumentException if the given component class name does not exist in the application's manifest.
• Android.Nfc.NfcAdapter.setNdefPushMessage(android.nfc.NdefMessage, android.app.Activity, android.app.Activity...), Android.Nfc.NfcAdapter.setNdefPushMessageCallback(android.nfc.NfcAdapter.CreateNdefMessageCallback, android.app.Activity, android.app.Activity...) and Android.Nfc.NfcAdapter.setOnNdefPushCompleteCallback(android.nfc.NfcAdapter.OnNdefPushCompleteCallback, android.app.Activity, android.app.Activity...) will throw IllegalStateException if called after the Activity has been destroyed.
• Accessibility services must require the new Android.Manifest.Permission.BindAccessibilityService permission or they will not be available for use.
• Android.AccessibilityServices.AccessibilityServiceInfo.FlagIncludeNotImportantViews must be set for unimportant views to be included in queries.

Applications targeting this or a later release will get these new changes in behavior: