Jeffrey Harmon has an interesting post over at his blog about his woes. His application was rejected with generic errors that do not explain in great detail how to reproduce the error. Finally, the errors have occurred in strange condition that would indicate that the testing is really thorough.
But if the tests really are that vigorous and Microsoft tests your application on all devices it can find (both ARM and x86, low-spec and high-spec), how come the following applications passed the tests:
Mind you, this is the default logo that is added to your application when you create new application in Visual Studio. You absolutely have to change it and use an image suitable for your application. They should have never appeared in the store.