This is only a small hint, but I just got burned by it with an update to my app using one of the multitasking notifications that didn’t exist prior to 4.0, which I forgot to do a check for before using. Luckily, UIDevice in 4.0 provides a new property (multitaskingSupported) to check whether the device is capable of multitasking. However, of course, this also doesn’t exist in previous versions of the OS.
To get around this, we can wrap it up with a category on UIDevice, using the method which Apple recommends in the iOS Programming Guide. This makes it much more convenient to call, especially if we’re calling it from a few different places.