Actually, one of my worst experiences on Android is with a pretty popular IRC client, AndChat. So, I'm on a Nexus S, I'm using AndChat, and I leave the app with the home button. It's still running in the background, of course - it shows in the notification tray, and it's in the multitask menu. So how do I completely close it? Do I:
A) Swipe away its notification that it's running in the background? Nope, that does nothing, the notification doesn't budge.
B) Go to the multitasking menu and swipe away its "card"? Nope, notification is still there and it's still running.
What I have to do is go back to the app, and hit the menu button - wait, no, the "exit" option isn't there on the menu if I'm currently viewing a chatroom. So I go back to the app, press the back button to get back to the main menu of AndChat, and then I can hit the menu button and choose exit to quit the app. Awful, awful design. Say what you want about iOS, but the way it's designed makes this kind of terrible behavior impossible.