On iPhone 3GS and iPhone 4, you can quickly switch between the applications you’re using; multitasking also allows certain applications to run in the background.
Double-clicking the iPhone’s Home button lets you view the most recently used applications.
The four most recently used application are shown at the bottom of the screen. Flick left to see more applications, if you have recently used many different apps, you may see 10, 20, 30, or more apps in that list. Our test phone currently shows 42 apps in the recents list. We are not sure what the limits (number of apps and/or amount of time before an app is not considered “recent”) – if anyone’s hit any limit(s), please let us know.
Anyway, the basic point is: Don’t worry, not all of these apps are “running.” In fact, most of them are not. Those 42 apps are the last 42 apps you used, they’re not churning in the background, sucking up your battery life. Think of them sort of like Han Solo encased in carbonite; they’re in suspended animation, so they spring back to life right where you left them when tapped. So, that app list is there for your convenience, not to stress you out, so don’t worry, be happy! You’re running iOS4 on an iPhone 3GS or iPhone 4, you lucky son-a-ma-batches! Your iPhone is taking care of multitasking, so you don’t have to.
If you don’t want anyone to see how many fart apps you’ve been running lately, you can easily remove an icon from the recents list: Simply touch and hold the application icon until it begins to wiggle, then tap the red minus sign icon for each app you wish to remove. The application is added to recent applications again the next time you open it.
[Thanks to MacDailyNews Readers too numerous to mention individually for the question.]