Just made my application store images to an SQLite database in background thread using NSOperationQueue and NSOperation and at first glance it seems to work nicely, but I have a few questions. 1. Do I need to have only one instance of NSOperationQueue in my application or can I have one for database things, another in charge of web requests and another doing some other stuff? Can they operate at the same time? Should they? 2. What happens when I receive -applicationWillTerminate: or similar messages? Do I need to check somehow if there are operations still in the queue?